well on a chevy the straight might look better. a gmc needs to be rounded.
but hell you need a grill i got a cheap gmc grill insert... 15bucks and its yours
i also got a BIG older chevy truck grill that goes headlight to headlight on a old classic i think 30bucks for it.
and as to the plastic valance weld not holding..... WHY WOULDNT IT? its plastic on plastic..... melt it together and its back as one piece again
and after you melt the outter pieces to be smooth just flip it over and use more scrap pieces to add a second layer to the back side spaced out over the repaired section. hell ill give you a old valance with tow hook holes... youll have plenty of practice with it AND plenty of extra valance to add bracing