On my 68, I have 10x29 goodyears that fit easily with NO trimming or rolling of fender lips.
The wheels I use are Centerline Autodrag 15 x 8.5" with 4 7/8" backspacing.
You can fit a larger tire on a 70 than on a 68 or 69, so you shouldn't have any trouble as long as you use the right wheels.