Back spacing question

I got a 68 Valiant Signet. I want to autox and drag race it a few times a year. Not worried about being competitive, just for fun. Bought Viking fully adjustable shocks to help with making work on strip/autox/street.

Tires and rims trying to make a decent compromise. I like the big little look and also pro tour too.

Looking to run 15 x 7 up front and 18 x 8 out back, looking at the American Racing torq thrust ll. Comes in both 15 and 18 kind of old school look at decent price.

And tires i want to run BFgoodrich Rival S 1.5 225 45 r15 and 245 40 r18 seems like a decent all around performing tire that I can get a couple of years out of them.

Now I'll being installing 11.75 rotor on a 2" dropped spindle with tubular upper control arm. And out back swapping axles (8 3/4) to have 5 x 4.5 all around.

My question what back spacing front and back do I need ?

I imagine the car will sit pretty low.