I am building a 35 Buick 40 series sedan. It is alsmost identical to a chevy master. My body was as you described yours. The structural wood was gone. The posts between my doors were dangling by the roof. I took a different approach. I built the structural part of my body before removing it from the frame including the doors and door alignment. I started by building two beams from 1 1/2 X 3 rect. tube that emulated the wood beams that tie the cowl to the rear arches. Before tieing together I installed the doors and jacked up the roof to ensure door alignment. Once that car is tied together it will be a nightmare if the doors do not close correctly. I then buit cross sections to support the floors and installed floors and rocker panels. Once all was welded up I removed the body.