Okay, further research indicates that it is from a Packard, around 1915; probably a Twin-Six.
Here is a pictorial representation of an original in situ, as it were:

Notice that it is mounted to the top of the speedometer - this explains the mount and the curious curve to the bottom of the mount, and the somewhat unique mahogany base that has been constructed for it to convert it to a desk clock.
So - does anybody have a source for Waltham parts? This one is missing the crown.
Thanks!
Cheers!
Chas.