Jim Haynes has put together a great rundown of the history of the Panzer tractor. I've posted it as a .pdf file in the Free Downloads Section.  It's #2 on the list. 

If you have anything to add, please send a note to info@panzertractors.com.

The Model A was produced in College Park, Md. in 1954.  Model A tractors will have a serial number stamped on the right side of the frame rail just aft of where it slides in to the front casting.  As far as we can tell, approximately 350 tractors were produced in College Park, of which we have documented less than 50 to still exist.  Copar was not good at keeping records, and most likely did not build the tractors in sequence.  The serial number on the frame rail will be 3 digits and most likely less in value than 350.  

Model A Panzers were all red, powered by an 8 1/2 hp Model 23 Briggs & Stratton engine and had cast iron pulleys on both the engine and jack shaft.  The jack shaft had the location "College Park, Md." and "Mod A." cast in to it, where later models had Laurel, Md.  Advertising literature shows it had 6x16" tires on the rear, although at least one confirmed original Model A has 8x16" tires on it.  

Because they were made of cast iron and succeptable to cracking, the jack shaft casting and pulleys may not be a reliable way to identify a Model A.  I have a Model A with a cast iron engine pulley and serial number stamped in the frame, but because the tractor was used extensively for mowing, it has a replacement jack shaft casting and a large pulley made of aluminum.  The rims had been repainted with yellow paint and had 8x16" turf tires on it.  However, when I took the tires off the rims, it was clear the original rim color was red. 

When production switched to Laurel, Md. in early 1955, the company began referring to them as a Model T102.  Because of existing stock and repair parts, newer models of 3 and even 4 wheel Copar Panzers can have a jack shaft casting that says College Park.  Jim Haynes (Dandy Sales) and I have had a lot of debates, and have agreed that only tractors produced in College Park should be called Model A.  All others were built in Laurel and are called by their T100 or T200 model designations.  

For example, I have a 3 wheel Copar Panzer that looks exactly like a Model A.  It has a serial number of 1947 stamped into the frame, but it is to the right of the tool box and not on the frame rail.  It also has an aluminum engine pulley.  Even though it says Mod A on the jack shaft housing, it also says Laurel, Md.  Because of this, it is a T102 and not a Model A. 

If you want to identify your engine, there is a great source of serial numbers for Model 23 and 23A B&S engines online at http://www.asecc.com/data/briggs/data4.html

I've added a picture of the info from that page below.  Click on the thumbnail to view.

Updated September 21, 2014

The T100 series was the evolution of the Model A. The T102 was produced starting in 1955 at the new Laurel, Md. plant. The 100 series has a single front wheel and is almost identical to the Model A except for aluminum engine and drive pulleys and yellow wheels and jack shaft housing. The jack shaft housing will say 'Laurel, Md" on it instead of College Park.  Although it may say Mod A also on the jack shaft casting, these were referred to by Copar as T102.

In 1957 a dedicated 4 wheel model called a T205 was introduced. This lasted until 1960 when Virginia Metalcrafters bought Copar and discontinued the line (see notes on the T220). The wide front end was adapted to existing 3 wheelers, so the steering shaft came out the right side and behind the front casting. Later T200 series tractors had improved front end geometry / design and the steering arm came out betwen the frame rails in the front.

According to a Technical Bulletin dated July 23, 1958:

Reinforcement of T102 & T205 Tractor Frames

Beginning with Serial Numbers 3-0066 (T102) and 4-0143 (T205), the frame on al 9 HP Panzer tractors have been reinforced by a rod between the tractor frame pipes and over the forward end of the differential.

It goes on to say that it was to reinforce the area where the frame pipes were welded to the axle housing - an area full of cracks on most tractors.  My model A had a pipe welded between the rails, but it was added by the owner (along with other reinforcements to the engine cradle) when it was restored sometime in the past 60 years.  

The T50 was the first in a line of 'small' panzers, starting in 1957 and running through late 1958. They have a couple of features of note:

• The grille, drive lever and pulleys were all cast aluminum.  The grilles were identical throught the T65 model.  However, there is no bushing where the steering shaft meets the front aluminum grille housing on a T50. This 'feature' often causes the steering shaft to corrode and not function. This was improved with an oil-lite bushing in the T55 front grille housing.
• No fenders on the rear wheels. Fenders were added later as a clamp-on option.
• A 4hp model A1200 Clinton engine was standard. This engine proved to be troublesome for both vibration and hard starting.  They experimented with the Kohler K90 4hp engine, and there are reports that some tractors were equipped with that engine as well.
• A plate under the engine extended to the left side of the chassis and supported the right angle gear drive, power take-off kit model 50PT.
• There was no isolated engine plate - the engine bolted directly to the frame.  This caused a vibration problem and the need for reinforcements on the T55.
• They were originally painted red / yellow / white.
   

These were very similar to the T50, and described as an improved version of the 1957 T50. These may be the most rare model Copar Panzer.  They started production in 1958, and were built along with the T50 and T60 as both 1958 and 1959 models.

Some characteristics from a sales bulletin issued October 17, 1958 (I paraphrased this, and did not include all items):

• Engine is a Model 1290 Clinton 4 hp.  This engine is balanced to improve vibration (over the one used in the T50.)
• Added stiffening bars on the grill plate and motor plate to reduce vibration.
• Oilite bushing installed in the grille casting for the forward end of the steering shaft.
• Thumb grip installed on the rod of the shifting lever.
• Stiffening bracket to correct the two open ends of the chain guard cover where it goes over the drive pivot.
• A spring is installed under the rod of the drive casting inside of the drive pivot casting to keep tension on the drive casting. (I'm not sure what this is, but that is what it says.)
• The brakes now use the hydraulic cylinder and plunger to make it adjustable.  The T50 was apparently the same as the larger tractors.
• Oil level plug is provided for the differential housingof the lift assembly to prevent the handle from moving too far forward.
• Hand grip is installed on the lift housing.
• A new hot spray paint system produced a longer lasting and more lustrous finish.  Color was red with white / yellow / black accents just like the larger tractors.
• A stop was welded on the notch quadrant of the lift assembly to prevent the handle from moving too far forward.

The 1959 model had a rubber isolation plate (see T60 description below.) The picture shows one that we believe to be a T55, but it has a Kohler engine on it.  The Clinton engine was not a good engine, so it may have been replaced with the Kohler.

The T60 Copar Panzer was an evolution of the T55 in that it had a "more powerful and practical 5 3/4 hp" Briggs engine. These tractors were also red / black / white / yellow in color. They had an engine plate extension on the left hand side of the frame rail for the Model 51PT power take-off gearbox, which is different than the 50PT that will fit on the T50 and T55. According to the sales bulletins, T60s were produced in 1958 and 1959. They and the 1959 T55 both had rubber isolated engine plates that Copar called "shock mounted engines." (SB5820).  In order to fit the Briggs engine, the hood needed to be raised.  The T60 and T65 tractors share a raised piece of metal welded to the frame under the grille casting.

When Copar was purchased by Virginia Metalcrafters in 1960, it appears they transitioned the T65 model into the T70 by changing parts that were cast aluminum into cast iron.  The drive castings and other pieces were slowly changed to cast iron first on the T65, and (with the removal of the word Copar from the front grille) the T70 was born.  They were probably trying to use up inventory from the T65 and produced a hybrid until they were out of Copar front grille castings.  Other than the aluminum into iron and some other improvements, the T65 and T70 were virtually identical.    

A 6hp "Easy Spin" Brigg & Stratton engine replaced the 5 3/4 hp version early on.  Easy Spin is a trade name for a mechanical compression release on the camshaft.  If you have an original engine, it should have a sticker on the starter housing that says Easy Spin.  A shaved head upped the overall compression, adding a remarkable 1/4 hp.  It retained the air vane governor which can be used to identify whether you have an original type engine or if it has been replaced by a 7 or 8 hp engine with a mechanical governor.  The engine was discontinued due to overheating issues in the early 1960s, and Briggs quit selling parts (including short blocks) for it.  For this reason, the engines are hard to find.  Fortunately, these engines were available on many brands of equipment from the 1950s, so you can find them occasionally.

Pictured is a T70bes that was purchased new in 1961.  Shortly thereafter, the electric starter stopped working, and it continued since then as a pull start.  The original mower deck rusted out, so the owner re-created it with galvanized sheet steel.  The drive engagement for the mower deck is much improved from the lever used on the T65 and older tractors - you just need to move it forward to engage the mower.  You can see a video of this tractor mowing grass at www.youtube.com/panzerclub.