Replacing 77 904 with 69 904

I just pulled my leaking 1977 904 trans from my 76 Duster. My plan was to fix the leak and overhaul it. It has a decent shift kit in it and a 5000 rpm governor. Was parked from 1994 to 2018 ! It was leaking from the bell housing area so I assumed it was a pump or converter seal. Well, when I pulled it I realized that the case is cracked and causing the leak. I found a local Mopar guy has 1969 904 from Cornet that drove fine. The price is right, but I want to make sure it will work. Anything that I should know ?