[restorevival]

I gotcha, that makes sense on the cam movement.

The sound quickly goes away with increased rpm. It is a very consistent somewhat slow rhythm, unlike the disorganized clatter of what high speed pinging sounds like. Does that follow your description of low speed detonation?

Timing is currently set at the 10 degree mark on the pulley. I'm pretty sure I only have manifold vacuum available (Stromberg carb), but will double check when I get home. On that note, I recall disconnecting the vacuum line to the distributor (why, I don't remember now) and there was no idle speed change, making me think that maybe the vacuum advance diaphragm is ruptured. Would that make a difference in this current scenario? (clearly needs to be addressed soon enough, but one thing at a time...)

Thanks again, geezer. This is all very helpful.