I first saw the pillbox style on Bedair's site long ago when I had a Griz G4000 (9x19) and was trying to sort out both the marginal (at best) lathe along with my total lack of skill. I started construction but never finished it. Like you, I upgraded, but my upgrade was a Rockwell 11x37, followed ultimately by another upgrade to my current 17x60. I think I'm done with upgrading, unless I can find a cheap clean DSG, L&S, or maybe a late (high speed) Monarch or the like.
Anyway, I've considered a number of options including those you've posted. If I build one now, it will probably be the C frame style. But, if you think about it, the compound itself isn't far from the pillbox ball turner, so as long as the pivot surface was clean and oiled it could be used as the base for a ball turner that functions the same as the pillbox. I wouldn't even consider doing that with the 9xN class of lathes, the compound on them is barely functional even when tight using a 4 bolt base upgrade, much less swiveling. But for a moderately small ball (maybe less than 2"?), I wouldn't hesitate to knock together some sort of lashup for my compound.
