Can I get 900F in a charcoal grill?

Alton Brown made a tandoor out of his kettle grill and a terra-cotta pot in Good Eats season 13, episode 17 ("The Curious Case of Curry"). It could reach very high temperatures.

I obviously can't link to that video, but there are plenty of similar videos on YouTube.

The Associazione Verace Pizza Napoletana, the folks who are responsible for certifying authentic Neapolitan pizza, say that "real Neapolitan pizza must be cooked in a wood-fired dome oven operating at a temperature of about 900 F." They do, however, say that it is possible to "produce a delicious pizza" in other types of ovens. Despite the fact that you aren't up for certification, you are on your quest for Neapolitan-style pizza, so it might be worth while to check out the requirements, even though it sounds like you are already familiar with some of them.

As far as getting high temperatures are concerned, I would recommend hardwoods. At these higher temperatures, you need to make sure you take appropriate safety precautions. While I have yet to get into making that type of pizza, I can say that I've successfully used wood to quickly boost temperatures of coals in fires and grills or smokers. I personally used chunks of Bradford pear that were no more than about 3 inches by 5 inches. More surface area means more air can touch your wood, allowing it to burn faster. Pizza oven maker Forno Bravo has some good guidelines for selecting wood on their website. They recommend

hardwoods such as oak, maple, ash, beech and birch, or fruit and nut trees, including apple, almond, cherry, pear and pecan. Fruit woods not only burn well, they are also fragrant. Some of the best-known wood-fired pizzerias swear by apple. Hardwoods weigh almost three times as much as softwoods, like pines, fir, cedar and spruces, so they give off more heat (BTUs).

An instruction manual for a Cajun Injector brand smoker, as well as various sources on the web, agree with this wood advice.

I found some interesting products made by a company called "KettlePizza." You may not feel like shelling out the cash for one of these, but if you look at their website, you can see that the design of their product allows plenty of air to get to the fuel while absorbing heat and radiating it back at the pizza from above. They say that their product can "cook a Neapolitan-style gourmet pizza in less than four minutes," as opposed to the "time not exceeding the 90 seconds" required by the AVPN, which suggests that KettlePizza probably won't take you over 900.

As a final anecdote, when setting up an inexpensive charcoal smoker once, I managed to (unintentionally due to high winds and a lack of patience) push the temperature of an inexpensive smoker to the point where the paint bubbled and flaked off, but this may have been related to the smoker's previous exposure to the elements rather than just heat. I didn't think to check the temperature at the time because it was obviously way beyond what is appropriate for smoking.

As measured by a Thermoworks IR gun thermometer, I've reached the maximum range on the thermometer (approx. 1000f) on some areas of the cast-iron grates of my charcoal grill on several occasions. I used oak lump charcoal in fairly large quantities (a few layers, started with an electric coil, supplemental charcoal added after the coals were convincingly ignited).

It turns out this isn't a very useful temperature, of course, but I did get decent results on a dry-rubbed tri-tip steak (according to those who ate it; I'm basically vegetarian). I seared each side and then set it up on a higher rack or a cooler spot (can't remember exactly which approach I used) because it was too hot. It was still quite rare in the middle even after increasing the distance.

I just have a rather typical sheet metal grill with an adjustable shelf for the coals and a cast iron cooking surface.