I am wanting to get a grille guard for my truck, which is a '88 model. The earliest truck I can find one listed for is '92-'96 trucks.

36688B GO Industries Black Knock Down Grille Guard Ford Bronco (1992-1996)

This is exactly what I'm looking for but the farthest back they go is '92, can I make it work without much modification? The site says it is frame mounted, but looking at the manufacturers website it looks like it bolts to the bumper. Are the two generations (87-91, 92-96) really going to be that much different?

FWIW, I don't really see this part bolting to the frame but rather bolting straight to the bumper. If that's the case then there should be no problem adapting it, opinions or input appreciated.

 

This one also says for 92-96, but it also says is bumper mounted. I'm not sure about the amount of difference between the 88 and 92 bumpers but this may be able to work for you.
Go Industries MODULAR GRILLE AND BRUSH GUARDS - JCWhitney

They usually have good customer service from my experience, they may be able to tell you whether or not it will work.

 

That's the one I was looking at. The website I found with the best price mentions frame mounting in the description. I don't think there is that much difference in the bumpers.

 

Those things are junk. The first time you tap something they're garbage, and take out your entire grille. The 87-91 and 92-96/7 bumpers are also not the same.