Front fenders. One needs replaced the other I believe can be fixed. The usual cab corners, well one corner anyway. The interior needs redone. I'm not sure of the rest yet since I haven't actually seen the truck yet but I have some pictures. The truck is about 5 to 6 hour drive from my home.
Front fenders are the same between the GMC and Chevrolet. Some say there may be some bolt hole differences, I did not have that problem when I did mine. The GMC will have parking lights in the fenders and the Chevrolet has them in the Grille.
If you are looking at a one ton GMC that needs some body work and you don't need to change out the hood, radiator and grille. Most of the Chevrolet parts will work. Cab corners are the same. Gravel shield/valence is not the same between the two trucks. You can weld on an engine mount to the front GMC cross member to adapt a Chevrolet 235 but not visa versa.
