Out with the old, in with the new...
Instead of trying to modify the 2 piece shaft original to the truck (4spd. granny gear trans., no slip yoke), it was just as inexpensive to go ahead and get a new, stronger, 1 pc. shaft (3 1/2", .083" DOM) w/new u-joints and slip yoke. Ordered on Friday am, and in my hand the following Thursday, from PST Driveshafts, in Clearwater Fla.
What's interesting, was the fact that the u-joints on the 12 bolt rear, that I took out, had smaller cups than the 10 bolt rear I swapped into the truck!
Lee