1969 Dodge dart rear tire fitment ???

The wheels are 15x7 with 4 1/4" backspace.
I mounted them on the axle and they are
1 3/4 away from the leaf springs and 1 1/2 from inside of the flattened lip on the quarter panel.
The 255/60x15s have a sectional width of 10.20 in their specs. Measuring from the center of the wheel, that puts me 5/8 of an inch from the leaf and 3/8 of an inch from the inside of the quarter panel. Thats if the tire will really blow up to 10.20" wide.