I have 275/60-15's on my dart with the springs moved in about an inch and I am running 15x8 cragars with a 4 1/8 in back space (this was the most they could do). I didn't have to roll the lip either. It is an extremely tight fit but they work.
I have a spring relocation kit in my dart (its a 67) when I bought it. It looks to be about a 1" relocation kit. I was able to get 275 60 15's under the back with cragar ss 15x8 with a 5 3/8 back spacing. They have about finger width of clearance.