Check out a box from a Land Cruser or Tacoma with a straight axle. I'm working on fabing a kit to mount the box forward of the axle by the core support, using a steering colum from a Jeep Cherokee with u joints & a shaft in between.
The arm swings verticle just like the stock box.

1949 chev 3100 3 window. 350hp/327/m21 4 spd, 12 bolt rear, power brakes, 3" dropped axle from Sid's. Disc brakes next.