Not sure what you had in mind for an adapter ... but that gave me the idea to make a fitting that slides over and is welded onto the existing barbs... with a tailpipe that accepts 1" hose.

In the meantime I remembered the name that Mainesail suggested, Brackett Machine in Westbrook. Without seeing the part he wasn't sure he could mill the barb down, but I'll ask him about making an adapter to accomplish the same thing.

EDIT: Just got a call back from Brackett, after sending a photo, they said they can either mill it down or remove it and put a new barb on, looks like problem solved. Thanks for the suggestions.

Max