another j head question

The increase is a percentage, and it is accross all rpm ranges. But, the greatest gains seem to be going from under 9:1 to over 9.5:1. Beyond that, the higher you start with, the less you gain, with arond 5% being the "norm". The best thing is, it helps low speed performance the greatest. That's where a street car needs it. Head bolts dont usually need any help, but you should be running a bottoming tap down each bolt hole and blowing out the debris. I have seen holes so full of gunk (Mopars the holes all end..not go into water jackets) that the bolts may have a rough time setting deeper in the holes, or the torque requirements will be way off. So clean them out, and chase the threads on the head bolts, and you'll be fine. If it's excessive milling (beyond say .100) then you could carefully grind away the bottom of the bolt for one thread or so...

That looks just like a low compression large chamber setup...lol. Jetting the 750 woint help that. A smaller carb that mixes better will. Think of all that carbon residue like a self sustaining compression increase!