Kurt, I got your PM and can now open your post too. Not knowing what condition the build is at, I can only give you width dems. My car is fully assembled and is modified. However the fram is still stock. Not boxed ,as it was in like new condition and the Chevy frame is stouter then the Fords.
Scinse you only have a week ,I would suggest also posting on Hotrodders.com and the HAMB to get maximum response.
I have found a lot of 31 Chevy owners on all three sites and all very helpful.
I will measure the frame widths for you tomorrow and post asap.
Where is the 1" gap on the doors. The body may be twisted or folowing the frame twist. It could be just shimming the body will help.
Also the sill s must be in good shape and probably are not. Have they been checked?
I cut out the bad sections on mine and replaced with oak. Its very hard to work with and harder then factory. You could get away witj a softer wood. Maybe ash or even poplar.
If you need any supplier info I have a good list of web sites available. Bob