welcome to the board.
if you do decide on the rotary engine for your project, i guess my first question would be, does the Sierra transmission have a removable bell housing? if so, you could probably get a Turbo II transmission and see if you could find a way to adapt the bell housing to fit. i know it's probably easier said than done though. the only other thought that comes readily to my mind is use the transmission from a B-series truck because i know people have put rotaries in them many times over.
obviously, you're likely looking at custom driveshafts either way.
good luck.