Good call Dana, that's definitely an old radiator cap. I worked at Grease Monkey for a couple of years in the early 90's and am well acquainted with them.
Might be simpler/cheaper to put a plastic bag over your head and rubber band it around you neck. If you can do 50 laps on Chair Peak in winter without removing it, wearing only running shoes and a wife beater, then you may be ready for the Kukuczka line on K2. Just don't buy your rope used in a Katmandu bazaar.