73' B3 340 Duster pro touring build

I went tire shopping today to narrow down my 18" tire options for the rear. I had Summit pull a 390/40R17 which I currently have on the car for comparison purposes, then went with 2 different 345/35R18's, a Mickey Thompson and one M&H, the Mickey's a little wider but a little shorter, they also pulled a 30"x12"x18" Mickey S/R Radial and a 29"X15"x20" S/R Radial. The 30"x12"x18" Mickey was way to narrow, but I liked the height. The 29"x15"x20" didn't have enough sidewall for the look I want. So it came down to the 345's...looks like I'm going to have to give up 1.5" in tire height plus the 1" in larger rim, maybe I can offset that by lowering the car a little more.

The tires on the cart are the 30"x12"x18" and the 29"x15"x20 Mickey Thompson's. The middle tire with the Arrow is my current tire surrounded by the 345's.