Why not remove your oil filter, cut it apart and inspect for metal piece's in the filter.
I would do that before pulling the engine. Since you are not sure if it is really knocking or not.
The knock may not be coming from the engine but somewhere else in the drivetrain. Harmonic's are hard to find because something can be making noise in the rear end and it will sound like it is in the engine.
I have chased these before and they are hard to find and will make you pull your hair out.
HI it may be messy but Maybe pull the valve covers and run it for a short time see if the noise stops, just to clear the valve covers from the mix..
I think you use a stethoscope but don't remember?
I've use two cork gaksets glued them together never had any leaks..
good luck take care be safe