Another issue is the running boards won't line up the same with the fender if you change to big truck fenders, there is about a 2" height difference.
If I've got my math right with big fenders the small truck running boards will appear lower than they should.

Grigg

•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-