I mentioned by ear procedure on timing because marks can be inaccurate. Balancers are marked differently, covers are also, etc. A by ear base and some inspection with a light as it’s revved will tell you how much advance is being ramped in as degrees difference.

repeat without the advance and you’ll know what the mechanical side itself is doing.

how much is too much depends upon fuel, compression, and combustion chamber design primarily. Sometimes as little as 30, sometimes as much as 42.

Id set it by ear with the advance hooked up then plug off the advance. That will drop where you are at immediately and force it to only use mechanical. If the spark knock is still there and mechanical was not crazy it’s not timing related then because it’s as conservative as possible at that point.