'68 Valiant - rear width question

There are several different 1/4 panel design on
this generation of A bodies.

On our 68 and 69 Valiants with stock width A body
8 3/4 we run a 15/10 with 5 inch Back Spacing or
15/8 with 4 Back Spacing. We run 9.0 x 30 slicks
or 10.0 x 28.5. slicks.