Have a good day folk's

Can anyone tell me what wheel size to run on the front of my 70 duster.I have a set of 8 inch with 4.5/8 back space and they rub the A fframe.I tried a 15x7 with a 41/4 Bs and the are very close.I want to try a 15x7 with a 4 inch BS,I think these will work but sumitt says to use a 15x7 with a 3.50 back space.HELP ME PLEASE.Thanks,Eddie if my email doesnt show up here it is. [email protected]