I would compare axle lengths that you have installed with
the axle lengths that you took out. Most of the time there is side to
side play in the axle that allows the axle to compress/expand in length
to let the suspension rise and fall as you drive over bumps.

I would compare the distance in both transmissions for how far apart
the differential is inside both of them. If it turns out that one differential is
"wider", then that would cause binding.

I have never heard (until now) that torquing down axle nuts would stop
the axle from rotating. Try looking on the back side of the hub for
something that is rubbing or interfering with the axle when it is tightened
down.

Plan B is to loosen up the axle nuts until the axle rotates, then torgue them
down in 5 LB increments until you start to feel some drag, then start
looking for the interference that prevents the axle from turning.

Plan C is to hit the internet searching for your tranny swap, and see what's
the most common reason for axles not turning.

Post up what you find, so we can all get smarter.-Bob