65 cable tranny-converto to slip yoe tailsahft?

I believe the internals are the same up to and including 65. For 66 the rear pump was eliminated, 65 still had it. This is likely the internal difference that you refer to.

Long tail shaft 904? I have only ever seen or heard of one length of 904 which is shorter than a 727 automatic. The 727 is much beefier and fatter and is likely what you are referring to as a long 904.

Yes, so much to learn......heck my information is probably wrong, LOL. Perhaps sometimes else can chime in.