Hi Rvt
You could tun up a couple of 1MT arbours and thread them to suit your chucks ,,,,,,,,,, if you dont want to make your own MT arbours , then have a look here
http://www.chronos.ltd.uk/acatalog/Chronos_Catalogue_Lathe_Taper_Tooling__70.html ,,scroll down to SOFT BLANK END ARBOR 1MT TANG END , only a few quid each ,,, it you dont have a Morse Taper Sleeves- MT1-MT2 (on the same page), i would get one of those too ,, then you can plug the 1MT blank into the 1mt to 2mt and stick it in the lathe head stock socket for machining and threading , that way it will come out concentric .
Cheers Rob