Tire Size Question on 68 Dart

Hello,
ANY help would be greatly appreciated!! I have a 68 dart gts H code I got a little crazy on with the motor and now I need to get a tire under it. We built a 505 stroker with stealth heads and a six pack setup so hooking up will be an issue. I want to run a redline drag radial on the car and I am not sure if these sizes will fit. I have not cut the car up at all but I would trim the inside lip if we have to for clearance. I bought a set of custom 15x8 steel rims with a 4.50 inch backspacing. I was going to add an offset shackle to get that .75 more clearance on the inside but does anyone know if these tires would fit in the whole. I would measure but the car is at the body shop 2 hours away and I wanted to order the tires but am not sure if either of these would fit. If anyone has tried them let me know or if you know what the max size is roughly on a dart rear wheelwell that would help alot. Thanks

size height section width tread width
275/50R15 25.75 11.2 9.75 w
275/60R15 27.75 11.1 9.75 w