I've asked a similar question and I've got some answers for you that might help
http://www.peachparts.com/shopforum/showthread.php?t=285097
I wouldn't go backwards in time - if you see what I mean - don't downgrade to an older transmission.
I think that if you change transmission adapters / get transmission adapters custom made, change "tail cone" sections on the end of transmissions, change bell housing sections on the front of transmissions, get custom made propshafts, hook up bowden cable assemblies if needed etc etc etc almost anything is possible - but it will be expensive.
In short this sort of work can be quite involved and expensive - you need to be keen to want to do it. There seem to be very few plug and play solutions... the easiest option is to stick with what you've got. But don't let me quench the desire to fit in a VW DSG or something like that (I would if I had the cash and the time!).