Your oven temperature (260 degrees C, or 500 degrees F) should be sufficient for baking a JerryMac pizza.
Not too long ago, member pwaldman suggested a new method for baking his pizzas, which he discussed at http://www.pizzamaking.com/forum/index.php/topic,6585.msg56478.html#msg56478
in relation to other methods he has used. Is the method you used like the new method he describes at the above thread?
Another possibility that occurs to me is to use a pizza screen, if you have one, together with a pizza stone. The stone would be placed at the lowest oven position and preheated for an hour at 260 degrees C. The pizza is initially baked on the pizza screen at the topmost oven position. When the rim of the pizza starts to expand and turn a light brown (the cheeses should be starting to bubble), the pizza is shifted off of the screen (which can then be removed from the oven) to the preheated stone to get the desired degree of bottom crust browning and crispiness.
A further alternative is to bake the pizza directly on the preheated pizza stone and shift it to the topmost oven position when the bottom of the crust is as you like it so that the top of the pizza can finish baking if such is needed (with or without using the broiler).
JerryMac's recipe produces a very high hydration dough (between about 65-70% by my estimation) so you may need to do some experimenting with bake times, temperatures, stone/screen options, and positioning within the oven to achieve the desired results.
Please keep us posted if you find a workable solution.