c3 has 13 trans pan bolts while the c4 has 11. that would be the easiest way to tell id think. the c3 was in all pintos 75 and up along with rangers, turbo coupes, mustangs, xr4tis...etc. it was fords "new" light duty tranny for smaller cars. im pretty sure all 71-74 autos were a c4. the only other auto pintos had was the c3. after the c3, c4s were mainly used for small v8s and i think some inline 6 motors...but im not for sure on that. ford then came out with the c5 in the early/mid 80s as, basically, a lock up version of the c4. the c4 valve body and convertor can be installed in a c5, but youd loose the lock up. c4 stuff and c3 stuff wont interchange..t hat i know of. after that came the aods, a4lds...etc.
blupinto, im sending you a pm.
bob