It sounds like you have a good handle on it, I'm sure your machinist will guide you to the desired result. I wanted to share a recent experience with a 68' 383 HP with the 10:1, and decided to follow the advice of a couple other roadrunner guys in phoenix, where it is really hot. I discarded the original Mopar cam and went to a comp cam. I wanted bone stock, .455 lift, and apparently the center line is different, and a few other changes in the specs as well. (I 'm not an expert in that area).Then I tightened up on the dist advance springs just a hair, and that engine will not ping with 91 octane Octane even when it is 90 degrees out. Once in a while I will add some 106 from the local station and mix, and that engine just runs even better. I did the same thing to my 69' 340 with the 10:5.1, and other than being a little less perky, it doesn't ping either. When I had the stock Mopar replacement cam, I couldn't keep either engine from rattling. it was Very irritating to say the least. This is just my experience, and I don't race, and I stick to the original specs on all my engines. Good luck with it, I am Interested in hearing how it comes out!