Thanks for the suggestions. I eventually managed to remove it.

There were several 'tricks' to the job. After removing the screws
holding the gearbox to the table, it was necessary to, little by little,
unscrew the two locknuts on the end of the leadscrew and slide the
assembly off of the leadscrew. Problem #1 was that you can only loosen
the nuts about 1/2 turn at a time, and #2 was that the leadscrew had to
be rotated to line the woodruff key up so that it passes through the
slot in the leadscrew bearing bush. In my case the slot was at the top,
the key was barely visible, and I didn't know it was there.

Once the assembly was removed, the worm wheel could be removed to give
access to the last of 4 screws that retain the motor to the gearbox, but
then problem #3 turned up 'cos the motor cannot be removed until the
worm on the motor shaft is also removed. It is held by a pin that is all
but inaccessible. When finally that was removed the motor was then free.

--

Regards, Gary Wooding
(To reply by email, change feet to foot in my address)