I would like to thank you all for your suggestions and replies. The old truck is now back on the road and running well. Because of a busier than usual scheule it has taken a long time getting it back to the land of the living.
The problem turned out to be kind of unusual to me. The timing gear on the cam shaft had come loose and slipped forward. It had hit and rubbed the timing gear cover. Presumably, when it came forward the timing was changed enough to catch and damage the valve train of that one exhaust valve only. The lobe on the camshaft was also lightly gouged. Everything else was fine. We replaced the camshaft and cam gear as well as the timing chain while the front was off.
I talked with a friend who built four cylinder race engines. He said that he had seen this happen on the Pontiac four cylinder engines but not on a six cylinder Chevy.
Now, Dominick, Where can I find those V8 sounds for a cassette tape player?
Again thanks to all for your help.
Rick