Take a look at the FAM, Section 2 Sheet 2.00 (3100) and Section 2, Sheet 2.01 (3600)
Those have dimensions of the respective frames. The look very similar, but I didn't check all the dimensions.
The 1950 Vehicle Information kit says the frame thickness is 9/64 inch on 3100 and 3/16 inch on 3600.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.