Looks like it'll work to me, design-wise anyway. Just be careful of that stone spalling under heat. I remember reading somewhere about that happening with granite while in my search for a better stone alternative to the store bought 1/2" thick pieces of crap that crack after one use. I ended up using an 1-1/2" thick hunk of sandstone for my kamado and it works great.
Maybe run the 3/8" plate right under it in case the stone does spall?
Good luck either way. I LOVE PIZZA!!!!!
UDS'-55&16, Akorn, Bar-B-Q Kettle, Drum Grill, miniWSM, cobweb-covered gasser. I'm JD.