Bill, I'm aware that this thread is 2 years old. I am trying to find a used VAC-370 (because it's been discontinued, so no new ones available anymore), and am also curious about the difference between the 370 and the 370B.
It seems that this thread didn't offer any light about your original question. Did you end finding out something?
Thanks, 73,
Marcelo W6EUH
Marcelo Bornscheuer - W6EUH