How do you determine "ride height" to make suspension mods??

Lots of good info here. I even like the MDF idea. If you are looking at buying Bullit wheels and then having them widened, why not just get American TT's with custom backspace? Could be close costwise. Like I mentioned earlier, check to see what the backspacing range is on the wheels you want. Example, if you decide that you need a 4.75" bs and all you can get is up to a 4.5", you are going to have to rethink the setup.
(Don't ask me how I know....)