Wheel/rear end

[gtome]

I'm curious how most guys go about this. I am going to be doing a 70 GTO and I will be most likely putting a 9" Ford rear, and I'm hoping for 305/30/20 tires for the back. I have to do the outer wheel house and quarters on the car, so I thought it might be a good time to massage that outer wheel house to accommodate a bit larger tire. So do you pick the wheels you like first, or do you get the rear first and get the wheels that will work with it? Seems like I can get a rear in pretty much whatever length I want, but wheels maybe only a few backspacing options?