Johnnyi.....I wish you lived closer to Denver...I like donuts. If your sure what it isn't....tell us what you think it is. I'm not arguing...just discussing. I've learned a thing or two from your ID's over the years. But I think if Garabaldi had two of these matching balls and sent them to me...I could build a fine working fly ball governor and send it back. One thing I wanted to ask Garabaldi is....when cleaned up...is this ball made of copper or brass

Its hard to tell but it looks like copper peaking through?
http://www.history.rochester.edu/steam/thurston/1878/f29p115.gif
Point M doesn't have to "just" be an attachment point between C & B. Point M can also be a pivot point where it attaches to that arm. This concept drawing doesn't show the arm between point C & B as being clearly ridged.
In this second example I believe this steam engine is a non-running static display and the flyball gov is stuck in the high RPM position. They have no place to go except down where the would be in 0 or low RPM, unless its actually running in the pic.
http://farm3.static.flickr.com/2428/3664610901_b3fb2a0f5e.jpg