When the body was on the old frame, the driver's door fit just a bit low but would close with a push, the passenger door was hanging and required some lift to get it to close, so they needed help to begin with.
When I lifted the body up a wad of washers fell out near the drivers door, so this issue was probably pre-existing. The drivers side floor had metal replaced at one time, and the body mount bracket as found on the passenger side is missing. The floor metal is fairly thick so I surmise they just decided to shim the difference lost when they left the bracket off.
There are two floor support beams that cross under the car, one just infront of the front seat, the other under the seat. When I lifted the body off I used 2X8"s running fore and aft close to the frame under those floor supports close on both sides, and slowly raised the body off the frame installing spacers between body and frame as I went. when I had room to run a 2X12" plank between the body and frame and spaced the 2X8's up to support the body on the plank. I then lifted frame and all high enough to put 20gal barrels [about 24" high] under the ends of the planks. I did somethin similar at the very rear with wood blocks and a plank on barrels, and then just lowered the frame out from under the body, and with little furnature dollys under the rear pulled it out from under and and reversed the prossess with the new frame. Other than the slow lifting and shimming the gapp between the body and frame to get the plank under, the body was only off the frame for a few hours. I would estimate the front plank was just about center under the doors.
I'll try to get some pictures, don't know how to post them however.
The new frame is a '38 and I thought I'd have an issue behind the axle, but measurements seemed to show the rear axle forward to be the same, and all the body bolts went through in the same place. The difference was the trunk areas where the '38 floor was different.