OK, well at least we now know that the laws of mathematics still work the same on both sides of the country LOL
I usually would guess not more than 3 cc's with the tulip valves, maybe 4 cc's tops? But I have not looked at each and every one....Or just touch up the chambers a bit. I took some 11.2 pistons to 10.3 by just judicious chamber grinding.
You could also easily go to a Felpro standard head gaskets at .051" thick. With that gasket and 3.4 extra cc's in the valve heads, I am coming up with 10.0. That'll get you down in the low 8 SCR range with a 268-ish type cam with 4-6 degrees of cam advance and a 112 LSA.