Ummm, yeah ...

A drive pin in the taper of the collet nose vs a key in the cylindrical body, and sometimes a remnant of milling it left in the thread, ala 5c.

2 piece adapter he made, hardened and then ground in place on the spindle.

Far more ambitious than I'd ever be ... but ... then there's the stuff my grandfather left behind. Drill press, looks like a couple castings and the rest from barstock? And a bench vise most likely from solid bar. Doesn't clamp very well. The fit between the jaw and body is too tight. I remember my dad demonstrating with a 1/2" bar, flipping the handle to lock it and it bounced back open.