[6pack] Missing under load

[John North]

Tuning following my engine rebuild...   When I put the pedal to the
floor in any gear, the engine misses badly, and smooths out when I
back off the throttle.   This is especially true at 2000 rpms or less.
  Once over 2500, it accelerates pretty well, still misses
occasionally.

I have 9.5:1 compression, Goodparts GP2 cam, smoothed ports.   I am
running with stock ZS carbs.

I have checked timing, points, plugs multiple times.   Have advanced
and retarded timing a few degrees.   Replaced wires, rotor, dizzie cap
with known good ones.   Changed carb needles for B1E.   All these with
little effect.   Dashpots have 5/20 oil in.

Vance called the GP2 a hairy cam, as I recall, and I am starting to
wonder whether that might be the issue.   Maybe it needs to run over
2500 rpms...

Any other experiences out there or suggestions for where to go from here?

John North