Have you checked the dividing head spindle and register for run out – it could well be OK?

If so then you should be able to manufacture the faceplate or chuck mounting plate on your lathe. You will probably need to make an adaptor for your lathe to replicate the dividing head spindle, but will care the faceplate or mounting plate should then fit OK on the dividing head.

If the head spindle and register are NOT OK then you have a whole different ball game to consider and you'll be into the scenario in your 1-3 in your post above, but if the spindle is out don't count on 3 as being viable, the MT socket coukld be out as well.

Keith

Turn the chuck register first . Ensure o/d and front face of backplate are machined true at same setting .

Mount backplate on a good face plate on lathe and set backplate true using previously machined o/d as reference .

Machine bore and thread .

You could instead clamp part machined backplate in a machined in place recess in a block of aluminium in chuck or on face plate if you want a super accurate job .

To true an existing dividing head backplate with minor errors use a dial gauge to identify locations of errors and amounts . Mark using felt pen . Progressively scrape down the high spots . Test frequently against a surface plate as well to ensure all over flatness .

MikeW