Is my Vacuum too low?

Greetings all.

Once again, I am back with a question where I have just enough knowledge to be dangerous.... and can use some assistance from the astounding bench strength here on FABO.
sorry for the long post, i want to be complete.

I have a 1974 swinger, with I believe a 1974 318... (I installed the engine, but dont have much history on it....)
I am reading a "steady" 16 inches of mercury Vacuum on my gauge. The needle vibrates some, but does not deviate more than about a quarter of a degree on the dial. (could be my crappy gauge)

This is a large improvement from when it was waggling up and down the dial as the engine surged and hunted.

I have:
* Swapped intake manifold to a factory iron 2 BBL manifold that was cleaned and inspected by a local engine rebuilding shop
* Replaced timing set with a double roller kit from Rock Auto. (probably went cheap here)
*Replaced Harmonic Balancer ( dang thing had no timing marks, I scribed one, after using a piston stop to find TDC.
* Set Initial timing at 12*BTDC ( Vacuum canister pulled and Carb port plugged)
*Set Idle speed to 750RPM
*Rebuilt and fiddled the Carter BBD carburetor.
*Installed new distributor, PVC, Plugs, Wires, Cap, Rotor.
*Started with Mixture screws 1.5 turns out. They are backed quite far out, to the point they seem wiggly and too far backed off.
*drank lots of beer, and fiddled with different idle speed/timing/mixture screws etc.



Engine seems to idle sweet, and smooth. Puts out a fair bit of black soot onto my garage floor, ( could be just till the choke opens fully) and what seems to me to be a lot of water.

No matter what I try I cant get Vacuum to raise higher than the 16 inches I am seeing on the dial. Is this a concern?

I cannot road test this tune setting, because I live in the frozen north and I am months away from ice free roads :-(