http://www.projectzerog.com/index.shtml
Theres a pretty good reference for wideblock swaps. You dont need to use the crappy 5spd or whatever came actually mated to the truck and I wouldnt suggest you do it... Starquest trannies are wideblock and will bolt right up to a wideblock 4g63/4 just like they would to the Starion motor. You can use a RX7 tranny too, but you'll need the bellhousing from a certain couple of years of Mazda B2600? pickup. The T5 and T56's are a good idea as well, I dont know for sure but I think the GM adapter plate will work for just about any V8 GM tranny. Look around the Project Zero G site, I think they have a link to a shop that sells convertor plates and other 4g63/4 RWD stuff for like 1/2 of what Buschur charges.
EDIT: Another thing you're going to have to think of is shifter position, depending on the engine/tranny you use you might have the stick end up in a weird spot.
Ooh, what about a rotary? My buddy has a '85 GSL-SE (first gen RX7 with the 13b) that we're going to drop a 383/T5 combo into... I'm sure he'd work out a deal with you for the whole engine/tranny stuff if you wanted it.
EDIT #2: Heres that site with T56 conversions stuff
http://www.midwestturbo.com/
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