Glenn, my taper bearing was in decent shape ( bless every operator that checked to see if there was oil in the headstock!) and I was able to remove any endplay by adjusting the bronze takeup nuts. I think reproducing one is beyond my skills at present, but could be done by an experienced machinist. My impression of the Mulliner is that it is a solid, fairly conventional design with no serious faults, and has all the abilities of a much more recent machine. I lost some threading sizes in comparison to my Sheldon 10", but gained capacity and a whole lot of mass. FYI, the Mulliner can be readily adapted to a South Bend overhead drive, if the original countershaft isn't with it, but I'll bet it is considering the steady rest survived,too.
If you pursue the 12" I'll put whatever information I have at your disposal; lathes UK has an excellent article on them, as well.
-James Huston