255-60's will fit on 15x7's on a 70 Swinger

Here I have Wheel Vintiques 15" X 7" (with 4 1/4" backspacing) wearing P235-70R15 BFG-TAs.

P235-70R15 BFG-TA Tire to Drivers Quarter Panel Clearance.jpg
P235-70R15 BFG-TA Tire to Passengers Quarter Panel Clearance.jpg
P235-70R15 BFG-TA Tire to Spring Clearance.jpg

I was originally going to replace with the same size tires, but have decided to go with P245-60R15 Cooper Cobra Radial GTs.

Here is a comparison between the two tires:

P235-70R15 VS P245-60R15.jpg