George,
Those in the pic's appear to be the old style pipe plug. Maybe they're original, but I don't know. The cat book is very vague as to drawing or description, and I've heard they may also could have been brass. I've been told by the Holt people there is a guy named John Matta (sp?) who is making reproductions for around $40 per.
But again, I'd like to know what they look like before buyiing.
What year is yours? Mine belonged to my Grandfather who purchased it in 1929. Restored and painted back to original gray.
Dave