Question about heads

The term 'bad spark knock' is hard to understand without hearing. Is it a REALLY loud knock? I'd be concerned that a valve is stuck and slamming the piston. (Old fuel, gumming the guides.)
Another possibility is the intake stuck open on a cylinder and the spark on that cylinder firing back up into the intake.
With the new cam, what oil did you use and did you follow standard break-in procedures with the engine revved, varying around the 2000 range, for 20-30 minutes?