it appears to be some sort of flow control restrictor to prevent coolant from passing through the heater core too fast for good heat transfer. I don't recall ever seeing anything similar in the almost 60 years I've worked on stovebolts, so I doubt if it's original equipment.
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!