17x8 with 4.75 Back Spacing.
255 40 17 in the rear
235 45 17 in the front
I started and maintain an advaced tire and wheel chart for 65-73 mustang that you can access here:
http://www.dodgestang.com/mustang.htm
I am building this database to try and take into account all the popular mods to give a much better idea to buyers what combos will fit on their mustang based on what mods. Check out the 71-3 sheet...its a little light because not too many people have submitted combos to me from that year, but if it helps great, if it doesn't after you get a combo, share it with me via the form link on the same page.