I used a shackle flip and axle on top of springs with A-body 8 3/4 to fit 12" with 4.5 BS rims with a 29x15x15 M/T in the fenders with bed tubbed.

I would suggest an A-body 8 3/4 with springs in line with frame rails. perches should be around the 41" center as a truck/a-body share the stock 43" perch center already.

this should allow you to go from a 12" rim to a 14" rim adding 2" to the backset of the rim then tubbing flush with the frame.

here it is before the bed