The wasp in the jampot is that there is nothing to stop the taper centre turning in the taper, apart from the jamming of the taper itself. This is not enough to prevent movement with milling loads, even cutting gears where the load should be end on. Also since the chuck or faceplate screws on, this can also move from milling loads.
So the taper centre on mine has been tapped on the small end for a drawbar. This is easy enough to do, just grind a little off the end first to take any surface hardness off. Most centres that I have encountered are only surface hardened.
The other fun thing with older Vertex dividing heads is that the taper is Brown and Sharp. I believe later ones might be Morse, and might even have a mandrel nose that matches the Myford thread, but mine doesn't, so has to have its own dedicated chuck.
John