Alright, Bert, I'll tell you what... these kinds of projects bring me a great amount of enjoyment. I'm willing, for now, to put the patent and potential retail price issues aside and, with an open mind, both see what this device can do as well as provide assistance in improving it. Be aware, though, that, regardless of how much assistance I provide, should you ever go into production and start selling it, there's a good chance that I will end up a vocal opponent.
First off, we need a lot more temperature readings than chamber air temp or case temp. We need stone temps, both hearth and ceiling. In an ideal scenario, we could get hearth bottom and hearth top readings along withe ceiling bottom and ceiling top, but, considering your setup, that may not be feasible. Drilling holes in cordierite tends to weaken it, but I'd really love to have a core temp of each stone as well.
A huge part of these bottom heat scenario devices is top to bottom heat ratio. You might be able to hit 800 in the baking chamber, but if the bottom stone is 800 and the top 700, then that's going to be a problem. The 2stone gets around this by using a very poor conductor for a hearth (fibrament). You can read about the differences between the cordierite you're using now and fibrament here:FibraMent vs. Cordierite (Engineering Data)
Be aware that cordierite can vary in composition, so the numbers won't match up exactly, but this gives you a good general idea of the differences.
Whatever gas grill you purchase, make sure you keep it pretty generic- no lower than about 30K btu and no higher than 60K. You might want to think about the fact that if the price point on this device ends up being a bit high, you will be targeting a higher income demographic, who will most likely have a higher btu grill.