Thanks for the replies. My research leads me to believe they were fitted with a knob as pictured below (Meddings drill but different model, best picture I could find off the net) This also matches the drawing as provided by John.
I have modeled one up and as best I can tell, the diameter should be about 1.25″ and should be about 3/4″ tall. I think i will make one and see how it looks. From a functionality point if view it doesn’t matter, but I like to restore them close to original if I can.

