727 - Driveshaft Jammed All The Way In

You won’t like my answer, but it is what I would do in this situation.
Remove the trans. Check engine crankshaft end play, to be sure it’s not excessive from possibly getting shoved forward.
Remove converter from trans and check trans input shaft end play to get an idea if there is any damage internally.
Disassemble the trans for proper inspection of thrust bushings, and really everything. If all ok, reassemble with a minimum of new seal kit. Frictions and steels too if any signs of excessive wear or heat.
Now complete the rear end install with a new driveshaft and new slip yoke.

There is a chance it will be ok, so you could do the rear end and new driveshaft and slip yoke only. If the trans goes later on, the only extra work is removing the driveshaft again, after towing it home.