Guy likely grabbed a converter for a 3/4 ton with a 5.7 gasser.

That is not a good thing.
Buttttttttttttttt....you can yank the Tranny and T case back out and down....The swap in the correct one.

A pain in the butt after all the work.....

If you don't pull heavy with it....It should be OK....JUST GOING TO RUN A BIT DIFFERENT.

Where does the lockup clutch apply ???

Should be at about 45-50 MPH AT MODERATE/LIGHT THROTTLE