A 50 4100 has a wheelbase of 137", same as the 3800 1 ton, which has a 9' bed. A 9' bed from the 1 ton might fit and look better.

For ideas on fender extensions and other nicely done metalwork to make a dually 1 ton check out this thread.
https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1107350/New_9ft_bed_progress!!.html#Post1107350

•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-