Thanks, guys.
First I made a nut out of 1 inch OD bronze hollow-bar. It is 20 mm dia. 6 TPI Acme thread (LH of course). And disassembled the machine to test that it fit the lead screw OK. The ears are brass flat bored to fit a shoulder on the nut, then soldered in place. Used the mill to trim things up, then cut it in half with the band saw. Back to the mill to skim the saw cut.
To mount one, I'll disassemble the machine again to clamp the mating part in the drill press to follow the existing hole for a roll pin.