Or the sheet metal cutting and forming machinery they have available can't handle 9'. I never asked but that's my guess.
They do make the other 1 ton specific bed parts as mentioned, so there is demand for 1 ton bed parts to some extent or they wouldn't even make those.

•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-