Originally posted by 1964 Oldsmobile 442
1st welcome to the board.
2nd You might get a better field of expertise in the matter if you joined a truck forum like Pirates 4x4 or 67-72 Chevy trucks(had 73 up forum also..)
and to try and help you here I go..
The one from your buddy would need to have the tail shaft changed with your existing tranny in your blazer. So it could bolt to your transfercase and adapter..
If you had time and money, I would look for a newer 700r4 "k" case and have it rebuilt.. The older the tranny of 700r4's the least amount of time it will last with the moving the weight of a blazer..
They just were never that great from the factory in the early years..
the case is different thick at flywheel cover, out put shaft is much shorter for the trans fer case, but as for the guts inside should be the same in clutch count 5 forward plates and 6 3-4 plates and will carry the same amount of weight in 84 you might find the 27 input spline rather than the later 30 spline count but both will work fine in the Blazer.....
Hope this helps
EDIT: I split airworlds message from the quoted message for better clarity.