Hello Houston. The fenders are different. But not so different that they can't be made to interchange.
My '56 3200 had a '56 100-250 GMC fender. I didn't recognize this until I pulled the fender and saw the "underside."
My advice would be: if the pieces are solid and the price is good, don't hesitate!
[img]
http://www.norcalspeedshop.com/_offsite_images/1956_01a.gif[/img]
BTW, '55/56 Chevrolet fenders are slightly different from '57 Chevrolet fenders.
