[Excaliber]

10 to 11" of vacuum is about all your going to get at idle AND cruise rpm with those specs. It will go lower when you step on it, higher when you lift off on it.

Vacuum reservoir cannister HOOKED UP CORRECTLY should help. The larger it is the more vacuum it will hold, but it will still only be 10 to 11" and that may not be enough for your brakes. Thats why some "hot rodders" use "juice brakes". Hydraulic motor to pressurize the brake system, Buick is well known for it.

Kicking up the idle speed and BASE TIMING rpm will also help. I wouldn't expect it to ever be much better than 12, 13" MAX!