Arthur Plumpton , Jan 01, 2011; 08:24 p.m.
I have the 2-c and it is likely similar to the 2-a except that I believe your two lens mount rotates to change the lens rather than slides, as on the 2-c. The 2-c lenses are mounted within barrels which have normal 39mm threads.
However, the problem with it, and possibly with the 2-a, is that the focussing barrel is too narrow to accept other more modern lenses without modification. A company in Germany that likely made the enlarger bodies for Leitz (Kienzle, founded in 1879) still modifies Focomat 2-c (and it appears also the 2a) focussing mounts and provides them with modern German (Componon or Apo-Componon) optics. I think the cost is about 5 to 600 Euros per mount modification and lens.
See the attached links:
See page 3
There may be other ways to adapt more modern lenses but I don't know of them.