Bob,
You should make sure it is a rod or bearing problem. How is the oil pressure? Try the spark plug wire procedure. These engines can make noises at times that can be serious and then not so serious. My '49 Chrysler started making a knocking sound which was diagnosed as a rod, or wristpin, or valve lifter, or loose timing chain hitting the cover. The oil pressure was perfect. Another mechanic told me that it could be a spark knock caused by a carbon piece glowing in one of the cylinders (he really said that). I was young and had hardly enough money to put food on the table so I gambled and used the car. Within several days the noise vanished and I ran the car another four years. What I am saying is to try to find the exact cause. Good luck to you.
John R