New to the forum,question on 91 grill update

[tuscani]

I'm sure this question has already been answered but I can't find the answer in the search. I want to put the 91 gmc grill on my 88 suburban. I've noticed that the core supports for the quad headlight system say except 7.4L or 454.
Does anyone know why this is and has anyone done the conversion on a Big Block truck? If so , which core support did you use? Do I have to find a used 91 core support out of a Big Block Truck? Has anyone put one of the Kits that the truck supplier houses sell? Thanks for the info