Not sure but I know you can also decrease the chamber CCs by going to a valve that has less dish. I know that you probably had somewhere around 8.6:1 CR with the pistons .100" down in the hole. I had 69CC heads on my '69 318 with the stock '69 pistons .030" in the hole and factory 9.6:1 CR. With the thin gasket, shaving the heads and the right valves you might be able to get 9:1 or close to it. Seems like I heard that you can also get higher compression by getting the right overlap on your cam?? Maybe someone else will chime in on the cam theory???