Erratic Vaccum Reading

The vacuum reading sounds about right for the cam and cubic inches but it should not flutter. It may drift around slightly but it should never flutter. My cam is almost as big as yours although not a roller and it holds 9 inches of vacuum fairly steady. A fluttering vacuum gauge usually indicates valves not seating properly. Your power valve is about the right size. You want it to be about half of the idle vacuum or slightly above. The old rule of 2" lower than idle vacuum is incorrect. With a pv that's 2" lower than idle vacuum it would open every time you bump the throttle causing a rich condition. Some guys run em that way but they run better with more headroom so they don't pop open every little throttle opening.

Don's right about the jets have no affect on vacuum.

BTW: Those are huge jets for a 750 even with your stout combo. How do your plugs look?