OK, looked up Speedmaster heads. They are supposed to have 65 cc chambers. According to Wallace Racing CR calculator, with a 4.03 bore, stock stroke, flat top pistons with no valve reliefs sitting .100 below deck at TDC, .039 head gaskets with a 4.18 diameter opening, your CR is 8.90 to one (half a point higher than a 340 with the same deck height, heads and head gaskets) (also half a point higher than a 360 with factory 72 cc heads, all else the same).
.027 thick Cometic head gaskets with a 4.08 diameter cylinder opening would bring that up a couple of tenths, but they aren't cheap.
Milling the heads .030 will bring the CR up about half a point, and you'll be able to get by without milling the intake side of the heads or changing pushrods. (OEM 360 steel shim head gaskets were something like .020 thick, so milling the heads .030 and running .039 head gaskets will minimally affect geometry.) A .030 mill used to be pretty inexpensive, but I have no idea how much that would cost today.
So unless I seriously miscalculated the CR, what you have isn't great, but it isn't a 7.5 - 8 to one dog, either.