Well I finally got back onto this thing a bit.
Cleaned up and painted some 4x4 leafs, ordered some eye bushings that were close enough to 521 front bushings that I could make them work.
L20B, freshened up 32/36 carb, and going with a late 720 4x4 5 speed trans that is the same length as the 521 trans, just have to swap it to a slip yoke on the driveshaft. also power brakes from a 720 4x4.