Help: What tranny do I have??

Is the transmission a ball and trunion?
Does it have a machined pad on it where a VIN might be stamped?
Does the side cover have webbing between the shifter arm bosses?
Why do you need to know what transmission it is? I assume it is an A-body 4-speed yes?
What you need to know is IN the transmission not on it. Open it up, and count the number of teeth on the input shaft. Then count the number of teeth on 3rd gear. Then look at the side cover and determine if the interlock detent holds the shifter forks with spring loaded levers. That'll go a long way toward telling you what you have.