3 different years, same transmission, which one should I use?

Currently in my garage, I have 2 transmissions, 1 is the stock transmission from the 1966 Barracuda w/273, then I have a 1968 318 with transmission attached, and lastly, my donor car is due this Saturday and it is a 1976 Duster with 318 and transmission.

Is there a difference/better one to use based on the year? I am going to rebuild the one I pick, I just want to start with the best possible core.

Thanks,

John