Has anyone replaced the chuck on a Boxford TCL 160 ?

The chuck itself works fine but I'm in need of some external jaws and I guess it's going to be impossible to get a set to match this chuck, so it looks like I'll need to replace the whole thing with one which has both internal and external jaws.

There seem to be a cap head bolt under each of the jaws, but the Boxford chucks I can find online seem to be threaded, so I'm not sure what's under this chuck, and I'm loathed to remove it just to find out.

I'd rather be sure that I can replace it before I disturb it.

Adrian.