I have a 1990 GMC 1/2 ton pickup 2 wheel drive. It has been lowered 4" in the front and 6" in the rear. I currently have a very old set  of 15x7's in the front and 15x8's in the rear. I am going to upgrade and would like to run 17 or 18 inch rims. I would like to get an 8" rim in the front and a 9.5 or 10" rim in the rear. I would like to know backspacing and tire size that will fit. I would like to have some side wall on the tire to go with the way my truck looks. Thanks for any info.