Have you tried it without cutting up the bumper? I measured (have two 3" on there now) and found that two 3.5" ones would fit side by side and leave a fingers width distance all around. And as they're double walled with a 3" internal diameter there won't be much heat on the outside surfaces.
The quads on mine are 90mm or 3.54 inches. Looks like it was designed to fit the stock location on the left but it touches slightly and vibrates on the bumper at low revs. I cut the other side out with a pair of tin snips and I thought Id have to get one of those bumper skins but it looks perfectly fine.