offset shackles (how big a tire)

hemi, I am running a very similar setup to mullinax on my '69 Barracuda. With the offset kit, I am running a 15x8 steelie with a BF 275/60/15. The only difference is that I added on .75" onto the backspacing which pulls the wheel in nicely. I have had trouble in the past with the wheel wells cutting into the sidetread and wanted to make sure it wasn't going to happen again. Good luck.