Diana, while the work Kenji did with the kettlepizza insert was pretty encouraging, unfortunately, we're not at a point where there's a set list of mods that will guarantee you great pizza. The biggest flaw with Kenji's results is that wood can easily reach foil melting temps, so you do not want to block the top of the insert with foil. At the same time, though, you want to block the gap with something, so you can force the hot air out of the opening in the side.
A round 21" stone should hopefully fit snuggly enough inside the insert to force the hot through the opening. If you go the 21" round stone route, here's a few notes:
1. Don't get it from California Pizza Stones. They sell a vanilla cordierite kiln shelf at double the price. Find a local ceramic supplier and avoid shipping charges or get a stone from Axner.
2. Unless you plan on grilling on the top of the insert, you don't really need an extra grate. You can support the top stone with 3 or 4 strategically placed bolts.
If a 21" stone does turn out to be a snug fit, then that stone, with holes for bolts drilled just above the opening, should both give you the ability to use wood without worry and make something equal to or better than Kenji's most recent KettlePizza offering. If you play your cards right, you might even approach something along the lines of Craig's recent NY style MPO testing pies:http://www.pizzamaking.com/forum/index.php/topic,20334.msg200768.html#msg200768
Since it works best to have the flame on the side, I think having a space to feed the fire with wood is counterproductive. Bottom stone on one side, wood log flame on the other.