After seeing the results of your compression test, and knowing no pertronix and a recent electrical tune-up; I would look at two items:
(1) As Dave mentioned, a vacuum leak
(2) Coil
The fact that is runs well on the road would tend to mask the effects of a vacuum leak (the air leaked would be insignificant at cruise RPM, but could become significant at idle).
A defective coil can still produce sufficient voltage at cruise, but insufficient voltage at idle. Coils, if bad, will have worse symptoms as the coil warms, as the secondary impedance will become non-linear.
Holding one's ones hand over the airhorn (personally, I would use the choke butterfly) could improve a defective idle caused by either of the above causes.
Jon.
