Model A radiators were never pressurized. I wouldn't leave vinegar in for a long time, but it's really a very very mild acid. It'd take a long time to eat away on any type of metal. In my opinion.
Something like rust911 would probably be best. chelate. It's somewhat a citric acid based. You can buy citric acid in bulk and mix it to whatever percent you like.
https://www.amazon.com/Milliard-Citr...ECZRBW2D7ZW17F
https://www.garagejournal.com/forum/...ad.php?t=69793
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