Piston pin bad ?

That noise is not a main or rod knock. Whatever was in that cylinder is probably now in your exhaust system.

Those valve seats are probably now toast. Can you see light coming through the valve seat when they are closed? Valves may be bent and were intermittently hanging open and that noise could have been the valve stem bouncing on the rocker arm. I would think your push rods on that cylinder would be bent. Roll them on a piece of glass.