Rebuilt 340 knocking sound
2 things you can do without tearing it down. Pull the valve covers, disconnect the coil wire. Use a remote switch on the solenoid wire to rotate the engine and watch the rockers. They should all rise and fall the same amount. Bent push rod, flat cam lobe will show minimal movement. If that checks out ok put it back together.
Get a good set of insulated plug boot pliers and/or good rubber gloves. and start the engine. Pull the plug wires one at a time until you hear the knock go away. That is your bad bearing.