Well, I'm happy to have some more progress to report.
I've now profiled all five dominos and drilled the holes for the M2 grub-screws - they just need tapping but I intend to do that indoors and by hand.
The profiling is simple but tedious, once the saddle & vertical slide were brought into position by offering the end of the end-mill to the flank of the original mount (damaged, but not on its flank) it was just a matter of mounting each blank on the profiling fixture (see photos), traversing the cross-slide to take a small cut, turn the blank ever-so-slightly, take the next cut and so on and so on!!! Getting and maintaining a routine was important - if the mind wanders it would be too easy to forget to de-clutch the lathe while re-positioning the work-piece and those fingers would be ever so close to that cutter!!!
Once I'd finished the profiling, I re-mounted the original mount on the fixture, swapped the end-mill for a drill chuck and the M2 tapping size drill and adjusted to align the drill with the grub-screw hole. Swap the original mount for each of my efforts in turn and drill the holes, this time only the saddle moves, the cross-slide & vertical slide stay put.
I'm hoping to see my neighbour tomorrow to ask him if I can use his belt sander. Profiling with the end-mill leaves a finish not a million miles from a fine knurl but before I declare that the end result I'll see how an off-cut of Delrin responds to the sander.
I set out to 'process' five blanks in case I lost any along the way. I've currently still got five usable parts although one got bored a little over-size.
I'll just have to be careful with the M2 tap!