How far in the hole 318 pistons

If you really want to find true compression ratio, you need to cc the combustion chambers and find the downfill volume of the cylinders. Production machining tolerances were sometimes very........ "tolerant", lol. Do a Google search on "half inch downfill volume of a cylinder" if you are unfamiliar. As for cc'ing the combustion chambers, you can easily fabricate a buerette from a piece of thick clear plexiglass and a graduated syringe. Windshield washer solvent works well because the blue color is easily seen in the syringe and under the plexi