jgame - I love it. Good for you. I especially like the differences between your implementation and mine: two underside burners, circular grill supporting the pizza stone, nice welding job, even the venting out the back. Please post your experiences as you continue to use the RPG.
A few comments from my version. I'm not sure what you used for a rotisserie shaft, but I tried aluminum, mild steel, and finally went to stainless with a bronze tophat bushing - which has been working well for some time now. I bought a cordierite stone for about $50 and felt it was a good bargain (after I broke the $18 thin stone I bought from Target). The cordierite is great, but the bottom profile is irregular with a thick disk at the center and a small rim around the periphery. For months, I used the IR gun to measure the stone temperature, always at the center. Sometimes, I'd find the crust charred and wonder why. A few days ago I figured out that if you are throwing pie 20 minutes after startup, the thinner parts of the stone may be 25F - 50F hotter than the center, and can scorch the crust. If you are cooking multiple pies, or using a longer warm-up, this is not an issue. Also a uniform thickness stone would work fine as well.
Your venting is unusual, and I'm not sure what effect that will have. From what I see in the picture, you have a cleaverly-designed vent out the back and some venting around the front hinges. The LBE guys vent at pie level. With two burners below and one on the side, I'm sure you have plenty of heat. You may have to back off the back IR burner a little to avoid charring the rim. Let us know.
Also, post up when you get more temperature data. I don't know your BTU numbers by burner, but 700F after 20ish minutes tells me you have some headroom.