I've been contemplating doing the same thing ('82 turbo in a '77), and it looks very plausible to me. I can't speak whether the shift points would work for the turbo (I suspect they would be close enough), but getting rid of the vacuum actuation I would think would be a plus. The '77 had the old tried and true kick-down cable/rod, so you could just switch all the linkages to the newer motor, with possibly a few mods to get around the turbo, and make it work pretty easily. It might not be as heavy built as the tranny used behind the turbo on the newer car, but unless you are doing burnouts, I bet it would hold up fine. It seems to be a very smooth shifting transmission from the small amount of driving I've done with it.

You would also need to do a little changing of the throttle linkages, as well as changing out the glow plug system to the newer pencil style controls.