Hey, Frazier,
I used a '98 Trans Am rear axle with posi and disc-brakes under my '59 Apache - might work on yours. I had to cut off the stock attachments and weld on leaf-spring perches, but no big deal.
It was a bit wide, so I used wheels with an inch or so extra back-spacing on the rear. This truck stops on a dime!
Regards,
