Mike....I posted some pics and info that might be helpful at the Forno Bravo site here (page 2): (http://www.fornobravo.com/forum/f24/anyone-ever-made-weber-grill-pizza-1511.html
The 8" stone hangs from the lid by copper house wire that I shaped to the proper form and attached to the lid with screws. This stone is discolored because it fell off onto one of my pizzas awhile back
so I have since then connected the copper supports with the stainless steel wire, problem solved. If you have access to a decent hardware store you should be able to find some sort of brackets that would be better.
Yes, the 2 lower stones simply sit on the cooking grid.
I cut the hole in the bottom of the kettle with just a hacksaw blade wrapped in duct tape, see the above link for more on that. You can use power tools or a torch if you have access to such tools.Copied from my post at Forno Bravo
I like to keep things simple so I took a 18" Weber kettle grill and cut an 11 1/2inch hole in the bottom. Mount the grill on a gas fired cajun cooker and put a 16 inch pizza stone on the top grate. I lined the inside of the grill with heavy duty aluminum foil, both top and bottom. This made a big difference with the heat retension and cooking quality. The gas burner will kick out 180,000 BTUs but I only run it at about 25%.
I use two stones on the top grate. I had one crack after 10 years so I use it on the bottom to buffer the flames from the burner, the other stone sits directly on top of the cracked stone. You can use tiles for the lower layer also.
I use an 8 inch stone mounted to the lid suspended with electrical wire. This helps cook the top of the pizza. Again you can use a tile.
You can use a 22" grill with a 19" stone also. I've used a 22" grill with a 16" stone and it worked nicely but it did use more fuel. The 18" grill is very portable and doesn't take up much space. The 22" grill will do bigger pizzas and also had the extra lid height for roasting chickens etc.
Cutting the hole in the bottom of the grill is pretty straight forward but there are a few tricks that might make it easier. I attached some pics to illustrate the process. I used a bare hacksaw blade wrapped in duct tape to prevent blisters. I cut the hole 11 1/2" but you can cut it anywhere from 10"-12" depending on the burner you use. I marked the circle using a plastic storage bowl centered on the grill. It took about an hour to complete. If you have power tools you could do it in a few minutes. The cutting blade will try to run in a straight line which is why you have to push down and shim the metal. This allows you to tilt the blade and follow the circle as you cut. Finish the proceedure by dressing the cut line with a file.
Let me know if you have any other questions.