That's probably the "clean air" fitting that was attached to a hydrovac brake booster. I've seen some of the hydrovac brake systems with about a 3/4" or 1" hose attached to the breather to prevent dusty air from entering the brake booster.
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!