SmokinGuitarPlayer, can this do 600 deg. sustained heat?
For Neapolitan, 600 indirect, won't work for the majority of stone materials. Fibrament, cordierite, soapstone, quarry tile and fire brick are all out of the question. What may work, and this gets into a somewhat theoretical realm (based on some pretty conscientious number crunching) is a cast iron slab. It would have to be pretty thick- thicker than those cast iron grills lodge sells, and you'd need two of them- one for the hearth, one for the ceiling. If you're doing one or two pies, I think 1/2" thick might work (with a few minutes in between to recover), but, more than that, I think you'll want 3/4".
Not that 1/2"-3/4" 14x14 (or larger) cast iron slabs are all over the place. If you could get one, though, I think it could be done.
Now, that's indirect. If you put down a fire brick hearth and fashion some sort of stone/metal ceiling, you could probably burn wood right on the hearth.
As far as 600 degrees damaging this cooker in some way.. I'm not seeing it. I've seen people attached blow dryers to webbers with no adverse effect.