I have attempted to adjust my distributor (purchased from Advance Auto Parts) to fit the specification given in the factory manual using a tachometer, vacuum pump, and timing light.  I have obtained results that are at least close to specification, but something is wrong.

If the car is idling in park and I slowly and gradually increase the throttle, the engine is smooth and fires evenly until around 900 rpm all the way up to something like 1400 rpm.  In that range, it misses, shakes, and is generally unhappy.  It seems to improve at higher rpms.  If I accelerate through that same trouble range with the vacuum advance disconnected, it does not miss or shake.  The vacuum advance is giving far too much advance at those speeds for an unloaded engine.

I have never known an engine in good tune to miss and shake during any reasonable range or load of operation, or, specifically, when slowly acclerated at idle in park.  So I conclude that something is wrong.  But it does not demonstrate the same problems when driving.  It is generally smooth and responsive.  At high road and engine speeds, say 70mph (3k rpm) it feels like something is off though.

The vacuum pickup on the carb (it's original, autolite 2100) is above the idle screw hole but below the transition holes, so it sees manifold vacuum almost the moment you ease off of the idle stop.  What is so puzzling to me is that all of the pieces of the system seem to be set according to their intended design, yet the actual performance of the system is flawed. 

Any thoughts about what, if anything, is wrong here?

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive