47-59 Wheel backspace and fender clearance

[bowt1ed]

Looking for insight regarding suitable, minimum clearance between wheel/tire and rear inner fender lip on my 57. Currently sizing American Racing's VN425 and would like to go with 20x12 on rear. Goal is to have as minimum backspace as feasible to maintain a deep dish look. Running a slightly narrowed 10 bolt with No Limit 4 link and bedsides cut out for tubs, so inside and top aren't an issue for clearance. I have 7 inches from mating surface to inner fender lip, so a 12" (13" overall) with zero offset should give me 1/2" clearance (to wheel). Plan on running @ 315/40 ish as not to extend tire width past wheels. Just not sure what a feasible space between wheel/tire and inner fender lip should be. Is 1/2" too little? Anyone running a similar set up/look, please share your experience. Thanks, Jim