Where can I get info on my transmission?

In my 1972 el camino, it was originally a 3 speed on the steering column, but someone added a new transmission with the shifter on the floor. I know nothing about this transmission only that it is a GM transmission. IS there somewhere I can enter the numbers to get info on it? Or if someone knows alot about GM transmissions I'd give you the numbers.

Still have three forward gears? If so, is there a side cover? Or a top cover? Or is it a 4-speed? Iron case or aluminum? More detail, please.

I didn't have too much info, but its finally out of the car and I'll be able to get some more info. I didnt look to closely yet, but I will tomorow Its a 4 speed with side cover, and iron case I believe.

4-speed, iron case (and tail housing) is a Saginaw. Iron case with an aluminum tail would be the Borg Warner "Super" T-10. The Saginaw is woeful. Won't take any serious power without falling out. The Borg Warnre, on the other hand, is among the best manuals of the era. Muncie (all aluminum, 7 bolts in the side cover) is considered the best one of the era.

I was wrong, it is aluminum, and is a muncie. I just don't know wether is m20, m21, or m22. I'm pretty sure its not an m22