I've been envolved in autobody repair for a long time and know from experience that if something has been bent/altered, nothing is going to go togeather easly. We know most of these old trucks saw some rough use or were just worn out. How "rough" was your truck was when you started out? Starting with the cab, is it sitting on the frame "square & level", do your doors fit? If so then line up the hood with the cowl. Setup the radiator support, make sure its "square & level", if not better check your frame. The fenders and aprons can be a bear if they've been wrecked. Ask a buddy to help push & pry while you start some bolts, leave everything loose so you can move things around. I'm not familar with the GMC grille, but can't see it being any tougher than a chevy grille! Sometimes theres little tricks that bodymen know, and we are softies when someone asks for help. Sometimes you just have to make "bodyparts" fit. I know some of the aftermarket stuff fits likes socks on a rooster. Consider this a Pep talk, hope it helps.
