Hey Keith,
I'm running almost exactly what you're planning on installing. I have a set of 15x8 Jeg's Sport Drag rims with 255/60-15 tires,and this combo would work best for a stock rear suspension A body. These back rims have 4-1/2" backspacing. The fronts are the same brand rim, but are 15x7, with 4" back spacing. The largest front tire you can use w/o rubbing or hitting something are 215/70-15's (which is what I'm using after some experimentation). KK