IIRC, Veco probably said ".19-.35". I am thinking it was shown with the plain bearing Veco .19. I would probably use a LA .25 or Brodak .25., or a '57 Fox .25.
I fly my "1st" version Veco Tomahawk with an OS .20FP BBTU. A Veco .19BB would probably be a good choice, also.
Big Bear