1976 Vette Tranny
Or here: http://www.keislerauto.com/gm/corvette.html
I have an LS1 and T56 in my '70. It's a lot more work (and $) than just swapping transmissions. If you want to go with a "budget" overdrive, people have put Mustang T5s in for well under $1k. (http://home.comcast.net/~ddecart/Transmission.html)
Hope that helps.
-Matt

