A car on a dirt track for racing, like your picture is one thing. This sounds like a driven nice day car, which would mean a vacuum advance system is needed a the build levelyour talking. However you have worked around it for so long.

Bucking no. It will increase advance from manifold vacuum and smooth out part throttle driving. Then fall away to the mechanical curve for WOT sprints.

there could be more to your problem but that is a red light for me.