Jazz on those piccys you posted doesn't it make more sense to put the 4th axis level slightly lower than the table instead of several inches above the table?

That way you can fit the same diameter stock in there without needing several more inches of z-axis travel.

PS this design looks like it is meant to do almost exactly what I'm designing my machine for (the 4th axis and the ability to fix pieces vertically for doing dovetails etc) Have you actually built one like this and does it work ok?