72 Ply Svamp Tire and rim combos

I just got a 1972 Scamp project. I'm looking for tire rim combos that will work without rubbing.
I found there are a few sbp rims available in both 14" and 15". I am looking at getting the American Slots listed by Summit wich are 15" with a 4" back space.
I am wanting to know if anyone out there has them or perhaps any 15" rim with 4" backspace and what are the best tire sizes to fit.
Thanks for the help...where I'm at most things have to be mail ordered and hate to make a bad choice.
SD