318 cam

I've seen those. IMO that doesn't come from the camshaft, but valve float and possible bad or inadequate springs. There have been as many cam grinds as blades of grass through the years. If the camshaft was the source of that problem, I think we'd know it beyond a shadow of a doubt. It'd be a lot more than a theory. I believe these guys sit around and think too dang much.
I think we can agree that spring surge source is loss of valve control and harmonics or natural frequency in the valvetrain. Could be flex in the pushrod or rocker arm.