Nick - I took a look at your new pictures and went back and read through your old posts on the engine placement and cab/radiator support relationship. From appearances, your '54 235 and 3 speed are correctly fitting on the existing frames front and rear engine support cross members. Since the 235 is the same length as the original 216, and the spacing of the first two cross members properly fits the Chevy engine and transmission, I think we can probably safely say that you have a Chevy frame, albeit most likely a '41-'46 considering the 115" wheel base. The longer GMC 228 and 3 speed would not fit in your existing frame.
The 2nd of your new pictures shows the bolt holes in the frame that correspond to where the rear transmission support cross member is supposed to be. Reading in both 1940 and 1941 Chevy Shop Manuals, the cross members are noted as "front engine support", "rear engine support", "The second cross member is of box member construction for its entire width. Bolt attachment to the side rails provides easy removal for the servicing of the transmission.", the third cross member "...supports the hand brake cable pulleys..." and "A single rear cross member is used." That covers the "5" cross members that make up the frame for both years.
Below is a picture of the bolted in cross member and still mounted transmission bracket which bolts to the rear of the transmission at the lower torque tube ball collar bolts. Interestingly enough, according to the Master Parts Books, 1937-40 All Commercial trucks (exc. KF) and 1941-46 all Commercial 1/2 ton trucks all used the same transmission support cross member and support bracket. The picture came from this
eBay ad. This one seems a bit on the pricey side, + about $70 shipping, but there looks to be others out there that may be better priced, so some searching may be in order.
I know this doesn't answer the width dimension inconsistencies from the 1941-46 Chevy truck frame specs, but perhaps that may not be relevant except when you mention the steering components. I think those are going to have to be discussed and investigated in a different thread in the
Driveline forum.
