1 have 15x8.5 with 275/50/15 DR's on a 88 LX and I didn't have to pound or roll anything. 5.0 back spacing on the rim (Centerline). On a 16x7 I would think 255.
I have 295/50/15 on stock rim, I also have rolled fenders and had to massage the inner fenderwell, I had to do alittle pounding, But now it doesnt rub at all and it look very mean, you cant tell I had to pound the inners..IMO
about a 245 is the widest you want to go. Any bigger than that any your tire mounter will have a hard time getting them on the rim.
You can get away with 6 inches of back spacing, but like 90mustangfan said you will have to message the inner fender wells. Nothing a 3# hammer and a little time won't fix, LOL.