Any rear axle change would also require changing the transmission and driveshaft as well, as the torque tube driveline would have to be eliminated. That said, late '70s-mid '80s GM F body (Camaro/Firebird) rearends seem to be a popular swap. Other alternatives include S10, or swapping the rearend center cection with the '55-'62 1/2 ton, which keeps the existng housing. There is also a 3.55 gearset available for the stock rear, which would also keep the stock drivetrain.
