It really depends on what size rear tire you are runnng, or most importantly, what size you may want to step up to in the future. I have a "68-"72 12-bolt in my car, and I'm in the middle of my notch project. I ordered 6.5" b.s. 10" wide wheels and yes a 275/60 will work, but it is still close to the fender lip. I am trying to fit a 325/50 drag radial and will no way work with that wide of a tire, unless you like the 4x4 look. My car is notched almost to the inner skin, and with the 325/50 drag radial I still have 1.5"+ between the frame and tire. My car is sitting for now, but I am going to order a set of 7.5" b.s. wheels to get the tire under fender. I am also putting in the tubs high and all the way to quarter panel so I can sit the car low with a 30" tire later on. Just my 2 cents worth...
Here is my car with 15x10 6.5" b.s. w/ 325/50 drag radial. Couldn't even move the car with the way mine sits. The fenderlip is actually sitting on the shoulder of the tire.