74 Duster wheel and rim .

I gents, I now have a 74 Duster with stock suspension,and plan on keeping it that way.I need advice as to rim size and tire.I like the 15x7 front and back,but what back spacing should i get so there is no problems.I would like a 255 60 15 rear and 215 70 15 front,any thoughts.Aftermarket rims is what i am looking for.
Author: Dons Dart