Obviously you can see differences between the common pans.
But how do you tell exactly what you have?? There are numbers on the case, and above the pan on the side. Sometimes they have tags with numbers as well.

There isn't some elaborate vin decoder somewhere for these is there?

What is the difference between a 200 and a 200 Lock-Up?
Other than the electrical connecting wire of course.

 

On the 200C and 2004r there are square metal tags permanently attached to the side of the transmission. The numbers on these tags will tell you what make, model, year vehicle it came out of. There's a Buick Grand National website that has tons of info about these trannies and you'll be able to decode your tag there.

The 200C is a light duty transmission and generally not highly regarded. The lock-up torque converter literally locks the converter so it will spin 1:1 with the engine. The non-lock up will have some slippage like all regular torque converts do.

The 2004r is an automatic overdrive transmission with an actual 4th gear. They put these in Grand Nationals and there's plenty of info available for building, or having one built, to handle high horsepower applications.