245/60/15's on 15X8 rims

Getting ready to purchase my new rims and tires for my 68 GTS but not to sure what will work on the rear. I'm looking at 245/60/15 on a 15X7 or 8 inch rim or 255 60/15's on a 15X8 inch rim. Suspension is all stock except air shocks right now but plan on taking them off and putting regular shocks on and adding a leaf spring to raise the back end. On the left side I have 11 3/4 inches between wheel lip and inner fender and 12 inches on the right side.
On your Coronet? They can handle 15x8's easy and the 255's work well on 8" wide wheels/ I have 255's on 7" wide and they work ok. 001.jpg 056.jpg