How to tell what ive got

Hey,help a brother out
im doing a tranny swap behind my 72 dart the motor is a 70 318 with a stock 904 behind it,i pulled the motor to put in my new 904,but heres what i saw the two dont look that much the same,im not sure what year the new one is from my uncle gave it to me as laster years Bday gift

old one is the left one

i noticed that the input shaft is smaller on the old one then the new one

also looking at the backs of the two the new one on the left dosent hav the same curves,or hump



Is there a way to tell if its a 904 all the numbers are gone of it mostly to smooth it out,uncle did it,
could this be a 727?help me out guys?
MIKE