Tires and wheel question.

My Valiant is minitubbed,and the springs are moved in 3".I`ve got 255/60/15 on 15x8 weld wheels with 5.5 backspace.I have almost 14" of space in wheelwells.When I had the old stock springs and installed b-body brakes(which makes the rearend width about 1/2 wider on each side)The 255s would rub up in the fenderwells on the outside.I put 1" over stock heavy duty springs from www.espo.com and all is good.I can easily go 325/50/15 with a 15x10 w/ 7.5.When I bought the Valiant,I new stock well were not gonna cut it.I`m sorry I can`t help with what fits stock,I have no idea.