Look in the parts manual,

Section 7.229
Picture http://chevy.oldcarmanualproject.com/parts/1929_54/413.htm
Parts listing http://chevy.oldcarmanualproject.com/parts/1929_54/421.htm

The 47-53 list one part number for commercial and utility... I'm not sure but that may be 1/2 ton through 2 ton??
54 has part number for 1/2 and 3/4 ton, and another for 1 ton, and two more part numbers for larger yet.

What does that all mean? Which 54 model crossmember is interchangeable with which earlier models? What's the real difference between the various 54 model crossmembers, are they different shapes/sizes, or only different material thickness(might be functionally interchangeable?), or???

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-