I run a 15x10 rear wheel 4-3/4 backspace with a 325-50-15 Nitto Drag radial on the rear of my 68 gtx. I do have the outside wheel lips rolled for clearance. You should be able to use a 15x10 wheel with a 5" or 5.5" backspace with 295-50-15 with no issues. I also run a 15x8 wheel upfront with 4.5 backspace and a 275-50-15 with no issues.