73 duster 17" or 18" wheels ?

I do have another question, yes my car does have the 7-1/4" rear. I am looking for a 8-3/4" and will be modifying the 7-1/4 for the time being so I can move it while work progresses. We are going to be doing a US Car Tool Mini Tub & Spring Relocation soon with the 7-1/4".

Without getting into what width your rear axle is mounting surface to mounting surface... I am assuming if I measured your 1/2" trimmed rear wheel lip to the mounting face of your rear axle I should be at 7"?? (Mine uncut is 5.5"). I am assuming the Mini-Tub will get me 14-1/4" of room over the 12-1/4" stock. I am aiming for an 18" x 11" +20mm Offset rim with the 8-1/4 rear. Later with the 8-3/4" I will just add a Hubcentric Wheel Adapter...