you will be pushing it with 8s on the Dart
may need the lip rolled or a massage to the inner wheel well...cut it back to the frame rail or mini tubb it
what rear axle you got?
my 68 dart needed 7" with 4 1/4 bs with the 74 7 1/4-4.5 wbp axle,could not get closer to the spring,had 1/8" clearance
needed 4 1/2" bs with 7" rims on the A-body 8 3/4 axle with moser axles and greens with the large B-body brakes,same thing here 1/8" clearance at the spring and tire bulge
it was centered in the wheel well good but could not get a wide rim or tire with out work on the lip and inside of the tire well
runing 12" rims with 4 1/2" bs now with 29x15.5x15 M/Ts on the A-body 8 3/4 and got a 1/8" clearance at the tire bulge and spring
not saying it cant be done and may vary car to car
its just what I got with mine
I think 4 1/2 bs is gonna be the ticket with what ever rim you run on the A-body with out moving the springs
good luck