Free US Mags...will they work for me?

So what is the ideal width and backspace for a 15" wheel on a car with the disc brake swap?
cant say, mine has a dana 60 w/ disc brakes. 3 1/2' offset on 8" wide wheels-dead center the 275 60 15 drag radials, w/ rolled inner lip. am goin to a 10.5' x 30" tall tire as soon as I get the car done. taller tire will help my cruising rpm w/ 3:73 gears. the 3/4" offset spring hangars put the springs right in line w/ the inner wheel house.