I'm gonna have the 3" body lift and 2" spacer shackles lift on my 91 Sport, and I need to know what the biggest tire I could fit would be if anyone knows.

i would say 33s... i havent done it but i am going to do 2" front coils, and rear warriors with a ranger main leaf and a 2" BL

33x12.50's wouldn't fit on my X with the same kind of lift. The tires kept on rubbing on the fenders. So to be safe I would go with a 32x11.50.

I have 33x12.50's on 15x10 wheels with the setup u r talking about. You can check out my pic in the Before and After section. The thread is titled "My '91 w/33's"

You'll have to do some trimming on the inner fenders though.