Help with offset..I don't want spacers

[cre8iv1]

I plan on running stock width front fenders and 1 1/4" wider on the rear of my 72 super.
I will be running the maxx struts for better clearance on the front,
I believe I should use a 17x7 with about a 40 et for the front
I want to use 18x8.5 in the rear...does anyone know how I can figure out the offset needed to fill the fender without the use of a spacer.

Thanks.