That is a factory-installed PCV valve system. It was standard equipment on some of the heavy duty rigs, and optional on others, I believe. It eliminates the road draft tube altogether, and recycles crankcase vapors through the intake manifold.
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!