[USAZR1]

I'm running 18x9's w/5" backspace (0 offset) and 255/35/18's on the front and 20x10's w/5.75" backspace (+6 offset) & 305/30/20's on the rear.

Just a suggestion but here's a combo that will should work fine w/o clearance issues, on your 71,
19x9 w/5.5" backspace (+12 offset) and 255/35/19 tire (3.5" sidewall) 26" tall. Another option would be a 275/30/19 (3.3" sidewall) 25.5" tall
20x10 w/5.75" backspace (+6 offset) and 295/30/20 tire (3.5" sidewall) 27" tall. Another option would be a 305/30/20 (3.6" sidewall) 27.2" tall