On my Unimat 3, of nearly 40 years vintage, the pulley thread on the vertical attachment is 12mm by 1mm pitch. The one on the lathe spindle is of course 14mm by 1mm pitch, so that you cannot use the lathe pulley on the vertical spindle. Later production may of course vary, and it would have been a sensible idea if they did later make them the same . I made a set of toothed belt pulleys for my machine, which is quite a worthwhile modification.
Incidently, the speed ratings on the nameplate are purely the product of somebodies fevered dreams and the actual speeds are totally dependent on the load anyway. This does not seem to matter much in practice.
John