I did something similar to this but had them made from aluminum stock
by a (next door neighbor) machinist. 2 through holes to bolt to the
Cole jaws where you normally attach buttons, 2 threaded holes (one at
end & one 2" in) to attach buttons. With the 2 button holes at that
spread I can get every width from the minimum of my Cole's to the
maximum of the extension. In other words, each position overlaps with
the next narrower and next wider. If you want a picture email me.
Also, email me if you want the machinist's address & phone. I'm sure
he would be willing to do more of these and mail them out.