340 with som problems

The first thing I would do is pull the valve covers and have a careful look to see if you punched a pushrod through a rocker, or maybe bent a pushrod. Next, I'd take a long screwdriver or piece of wood and hold it against various locations on the engine to determine where the knock is originating. The other thing to check, is the sound at camshaft speed or crankshaft speed. The answer to that should narrow down your search for the noise. Good luck.