A-904 Compatibility and changes?

Wanted to see if someone knows the difference in years of the 904?
For example rebuild kits will list 1960-1971 and 1971-1992.
Other than the obvious linkage setup on the outside of the transmissions what changed internally?

I have a 1971 /6 904 and 72 /6 904, yet the kit cuts of at 71 and the other starts at 72. Are the cases the same and just the internals?

Still learning automatic transmissions.

Thanks