What's the condition of the spare assembly? It would be a lot simpler to just swap the whole transmission than trying to do a partial repair with the trans still in the vehicle.
Jerry
The last time I lay on my back in my driveway (with the truck up on jackstands) and bench-pressed a transmission into position...was the last time I'm doing that. I had hoped it would be more manageable to just swap the overdrive units.
The condition of the spare transmission is wholly unknown. I bought it a few years ago from a fellow stovebolter, and it's sat in my garage ever since.
-Kevin