I broke my oven doing that and ended up spending $600 to replace the control board.
Marlon, I wasn't aware that you broke your oven. I'm sorry to hear that it cost you so much. I didn't say anything at the time, because it seemed like you were very happy with your results, but I believe you could have matched/possibly even improved upon your results, along with stressing your oven less, with a slightly different configuration. My suggestion would have been to raise the hearth to the top shelf, go with half inch steel, and only use the frozen towel to push the oven to 625. The closer proximity to the broiler, especially your broiler, would have compensated for the lower ceiling temp, the half inch steel would have provided excellent Neapolitan undercrust char at 625 and 625, for a 550 oven, is the mildest/safest of hacks.
This is all moot now, of course, since it sounds a lot like you've given up Neapolitan in a home oven for good, but, if someone else had your broiler (one in 200 people, I'd estimate), then I think they could take your experimentation a bit further while not putting their oven in jeopardy.
On the NY suggestion, I agree 100%. I strongly feel that NY, done well, is way better than longer baked Neapolitan dough.
Camaro, if you have a broiler as powerful as Marlon's (see his link), then I definitely recommend experimenting with it. If your oven is like most people, though, then it's time to either play your hand at an LBE or go the mortarless route. You don't really need masonry skills for a mortarless oven. No matter what you do, it's always going to be a bit of a game of chance. Marlon's broiler (1 in 200), Neapolitan in an LBE (1 in about 100), Neapolitan in a mortarless oven (1 in around 8, that we know of, but, more likely 1 in 50) are all gambles. A well planned mortarless might be the secret to Neapolitan bliss, but it's really too early to make any guarantees that a specific design will produce results.
A 2stone should get you to Neapolitan, but, if you're going to spend $2K on that, you might was well spend another thousand and get a wood fired oven.