And what I *don't* see anywhere are ER collet chucks with a
threaded back to fit on common lathe spindles directly. Perhaps a Morse
Taper for centering and a collar which matches the threaded spindle for
pulling it in without fitting a drawbar to the lathe.

I don't need it -- but others might. Let them speak here.

Good Luck,
DoN.

Been there done that, i settled on TG collet chucks and collets.
Bargians found on ebay allowed me to fit my logan lathe with a
TG-200 collet chuck which has a 2" capacity. The chuck started
life as a CAT50 taper and was ground down to fit the taper on
the logan. I also have a a flat back TG-100 collet chuck that
is handy, they do show up on occasion on ebay along with
collets.

Best Regards
Tom.