You could just buy a used tranny.
Here is a link to hundreds of junk yards data bases and what they have in inventory.
www.car-part.comIn the 2nd field select:
Chevy Truck-10 Series (1987 Down)Next page input range 47-55,
I not sure what years Chevy used the same 4 speed tranny. I am pretty sure they used them from 47-55.
This is what you should end up with.
Link for 47-55 transmissions Hope this helps,
