Well, Lou, I removed the drill stop collar from the Rockwell/Delta
radial drill press, and the mortise attachment fits on the quill
precisely! Now the next thing that I need to do is put something into
the chuck, in order to help center the mortise attachment, then replace
that with the drill bit and the chisel, and it looks as though I might
be in business!

If I used a bushing that was 1/16" thick, wouldn't that work? :-)
Thanks, Richard