Ibrahim, that's great news about the rotisserie burner.
Even with a rotisserie burner, though, this gets a bit complicated.
The closest anyone has gotten to Neapolitan bake times with an IR burner grill is Craig. The simplest solution would be that if you can match his heat output and use his stone,http://www.bakingstone.com/
you can achieve his bake time. The problem is that his stone is only made in the U.S. and to have it shipped to Kuwait would most likely be incredibly expensive. Not to mention that this stone is both physically and thermally very weak- not only might it not make it to you in one piece, but the intensity of the IR burner might do it in after a few bakes. It comes with a metal shield that protects it from heat from below, but there's no guarantee it can handle intense heat from the side.
There's a chance that a fibrament stone might not be necessary, but I can't say for certain. Fibrament has a special trait- it's low conductivity allows it to be used at much higher temps without burning the bottom of the pizza. The question of the day, though, is how much these higher temps actually add to the top heat in this scenario. In order for a ceiling to play much of a role in browning the top of a pizza, it has to be either extremely hot and/or extremely low. As you ramp up the heat of the grill (Craig was able to hit 900), I don't think the ceiling is either hot enough or low enough to provide much browning. I think, from a top browning perspective, you're relying almost entirely on the IR burner, not the heat radiating off the ceiling of the grill.
In other words, if, say, you can cook the bottom of the pizza in 2 minutes at 750 with a fibrament stone, and a kiln shelf, because of it's conductivity, could do that same 2 minute bake at 700, I'm not sure a 750 degree ceiling is going to brown the top of the pizza any faster than a 700 deg. ceiling.
You could add a lower ceiling to the scenario, but you can't go that low or you'll block the IR burner.
Do you see where I'm going here? A low conductivity stone (Fibrament) might not be essential to Craig's bake time. Or it might. My gut is telling me no, but I'd hate to have you buy something really conductive like steel plate, pre-heat the grill as low as 650 and end up with insufficient top color.
Quarry tiles are actually less conductive than fibrament, so if I'm wrong and lack of conductivity does help (you might be able to bake at 825 with the quarry tiles), quarry tiles would be ideal. Unfortunately, quarry tiles are incredibly thermally fragile. In this kind of setting, they'd just fall to pieces.
Firebricks can, depending on their composition, be less conductive, and, like quarry tiles, might be suitable in that 825 realm, but the amount of thermal mass they bring to the table would require an obscene amount of fuel and time to thoroughly pre-heat.
Then there's also the question as to whether or not you can reliably hit 825 with this grill and whether or not Craig's non manufacturer recommended approach might, over time cause any damage to the grill itself.
If you're feeling adventuresome and don't mind going through lots of propane tanks, then I think firebrick splits (1.25" thick) are the answer.
Otherwise, if you want to play it a bit safer, but, at the same time, slightly risk extending the bake time (and potentially leaving the Neapolitan realm) by working with a cooler dome, then I recommend a cordierite kiln shelf, as Don suggests. If you do go with a kiln shelf, I wouldn't necessarily go too thick, as the thicker the shelf, the faster the bottom cooks, the lower the pre-heat temp. Since the material itself is already requiring a lower temp because of it's conductivity, I wouldn't take that a step further by going too thick. 3/4" thick should give you pretty good recovery times- if you feel like you might be baking more than, say, 6 pizzas at a time, then 1" might not be the end of the world.
Before you buy anything, though, I would close the door to the grill, crank the burners and see what kind of air temps it can maintain. Could you tell us a little bit more about your 'digital thermometer?' For what you're trying to do, an infrared thermometer is critical. Besides air temps, an IR thermometer will give you ceiling temps and wall temps.