17" or 18" rims on Demon?

So I am looking for some help on my wheel and tire set up:

here is what I have:
72 Demon --
Rear: Mini tubbed and spring relocation kit to the frame rails. running SS leaf springs -- 8.75 rear end that is 55 1/2 total axle flange to flange, 50 3/4 housing.
Front: running stock 73 disc brake setup currently but will eventually be moving to an alterkation set up.

Wheel Combination I am leaning towards:
Wheels will be Mustang Bullitt Rims:
Rears: 18"x10" -- With A Mickey Thomspson #6671 - 28x12.00R18 Sportsman S/R Tire
Front: 18"x8" -- With A Mickey Thomspson #6670 - 28x10.00R18 Sportsman S/R Tire

Any thoughts on the fit??? Or whether I can fit even a larger tire in the rear???