The F-370 has a standard GVW of 19,500 pounds and optional up to 22,000 pounds which puts it on the fence between a 5000 Series 2 ton and 7,000 Series 2-1/2 ton.
Your '59 100 with Cast Spoke wheels is more than likely rated at 25,000 pounds GVW, so swapping axles will be a GVW down grade.
FYI, Low Cab Forward (LCF) is a Chevrolet thing, GMC just called that style the "F" Series.
Mike B
