SBP to LBP Cragars

I am doing a conversion from SBP to LBP on my 71 Duster. I would like to go with a set of 15" Cragar SS rims. When I enter 76 Duster (what the front disc were from) The app says not compatible. What size do I need to go with? I thought 15x8 5 on 4.5 would work but they say not compatible.

try a 68 furd buttstang.