These engines were made to work for a living, and people didn't care if they rattled a little bit. Running an engine all day long with a full load on the truck and wide open throttle was what a GMC was designed to do. The exhaust was too loud on most of them to hear a rocker arm making a little noise.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!