Wheel size and backspacing

[biohazardbill]

Looking around for ideas for what is a good tire size for the truck, I found a truck that has a similiar if not dead on stance as to what I am trying to do. Reading through the build thread he was using 17x7.5 wheels with a 15mm offset. In addition to these wheels he was also using a 3/4 inch spacer.

This being said what backspacing is needed on an 8" wheel to eliminate the spacer and achieve the same look keeping the outside of the wheel where his sat. Hopefully this made some sense. How about possibly a 7" wheel as I may do that on the front not sure yet.