255-60-15 MT drag radials on my 68 dart

I thought I would have to trim or roll the lip when I ordered this size, so far I have not but I need to lower the tire pressure to 18 and see if that changes anything. This size tire on a 7 inch rim makes the section width about .2 smaller, so right around 10 inches. About half the posts I read said they fit no problem, the other half said they will not fit without modifying outer lip and/or moving spring inboard. I wanted a taller and wider tire, the old BFG 235's would not hook with small shot of nitrous and it was spinning about 6,800 rpm through the traps, these tires should help a lot.