Rim size and backspace, housing lenght for minitubs?

I've done 48" and 47" on narrowing the rear end in a dart. With both I used 10" weld wheel with 5 1/2" back space. On the 47, I had to use 5/8" spacer but did it because a 12" wheel with a 6 1/2" back space works. It's tight! but will fit. I like my wheels to be centered in the tub that's why I did these lengths. All I can tell you is MEASURE,MEASURE,MEASURE!!!! Before you commit. It's an costly mistake if you get it wrong. The wheels you run have everything to do with your axle length. Russ