Rebuilt 340 knocking sound

You may be signing up for heart surgery when all you have is a bad connection .
I have seen bad electrical systems cause misfiring, low rpms, crazy oil pressure readings and knocks . The orginal regulators 6 volt for dash gauges are a joke. Plugged oil pickups are possible but the builder would have to be responsible (stupid) if they didn't inspect it.

A hammer wants to hammer a nail .
Good luck