acceptable bs on a 18x8 mustang wheel...66 cuda

I used a wider (ford 8.8 rear and mustang "bullitt" rims with lots of backspace (4.5"?). I mocked everything together and measured ..alot! Now my 65 is 4 wheel disc, 17" 5 x 4.5 rims, 3.73:1 l.s. diff. The 8.8 is full width from an explorer.