So what you are experiencing is knock when vacuum signal DECREASES with throttle opening...generally meaning either to lean a mixture or too much timing. You already have full vacuum signal, and full vacuum advance, at cruise RPM. Delaying onset of vacuum won't help.
Have you tried driving it with the vacuum advance plugged, or changing source from manifold to ported or vice-versa?
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
