I have a 72 Malibu with drum brakes that originally had 14X6 rally wheels with F78X14 tires. I went to 15X8 American racing mags with P235/60R15 Goodyear Eagles all the way around with no clearance problems front or rear. You could possibly go a little bigger on the rear but I wouldn't on the front. Start mixing up sizes and you can't rotate the tires though. A true 70SS should already have either 15X7 or 15X8 rims on it originally.