Wheels???

[prostreetdrag]

Ok i i know its been covered a million times on what can and cant fit as far as wheels but my question is there a proper way to measure for wheels and proper backspace? every car,frame and rearend fits a little diffrent and i dont want to buy wheels just because they fit one persons car because it doesn't mean it will fit mine the same. I have a 9 inch ford built for my cutlass I had it shortend an extra 1/2 inch on each side compared to stock length and im doing a frame notch,full tub and also rolling my fender lips. I want to get the best fit as possible i will end up going with a 28 or 29.5 slick on a 15x10 wheel. but im looking for a correct way to measure for the correct backspace to get the fit i need. again i dont want to go based on what someone else runs or eyeballing it but is there a way to make a templete and a straight edge to get the correct measurement??