Change the rod bearings and cross your fingers!

You said the knock is on one side? At the head area? Does it go away under a load? How is the oil pressure? Had a 340 knock at idle and when ever decelerating but went away under a load It was a bad piston pin hole. It too was on one side under the hood. Usually a bearing is lower and can be heard coming from the pan.

Unless you have a spun bearing and both are in the rod? Then the piston could be hitting the head. Pull the plug wires one at a time while idling to locate the cylinder if its a pin you'll hear it. If the oil pressure is real low then you know its a bearing and I wouldn't run it.

Also had one come here and he dropped a carb nut down and it was squashed/molded into a piston. knocked like crazy