The way GMC did was like this, all cheby and GMC hoods are the same, but GMC used the 67-68 style fenders through '72, but since in '69 the general changed the sloped hoods (67-68)to the different ones (69-72) GMC had to add a front bar on top of the grille to make up the difference in lenghts for the hood, I have a pic of a 69 GMC, notice the chrome bar in front of the hood, 67-68 GMC didn't have that.
Hope this made sense to you, sometimes it doesn't to me lol
EDIT: forgot the frking pic