Mickey Thompson pistons

Okay, ALL of this is assumption/Wild assed guess, as any actual measurements can throw off any of these calculations.
If that .085 step was full size, it would be 20cc. It looks like about a quarter of the piston top, so I'm gonna figure 5cc (actual measurements would be required for accuracy)
So, these assumptions:
4.28 bore
3.75 stroke
90 cc combustion chamber, 906 head.
5 cc dome volume
.038 head gasket compressed thickness
4.375 head gasket bore diameter
.000 deck height (yours will be a few thousandths either way)
1cc for "other" (Wallace calculator)

I get 431.6 Cid, and 10.17cr

Now ALL of those numbers are very changeable (dome removal, valve relief install, deck height actual, milled cylinder head, actual cylinder head volume, etc. etc).
Just an educated w.a.g.
Edit: you won't have to remove the reverse dome with 906s, you would with 915s, closed chamber Eddie's, or trick flows.