69 valiant rear 1/4/tire and wheel measurement

sorry for the 'tarded heading....im tired and need to hit 'er but cant stop thinking about this car...just wondering on backspacing in the rear....i have a measurement of 5 and 3/4" drum to spring and 5" drum to fender (now on a 69 valiant there is the fender lip...and then a little but higher than that is the actual fender....the 5" number is to the actual fender....any thoughts or testimonys here bortha's?...valiant kid needs help on uncharted territory!