I know exactly what the poster above is referring to. However, I have a DISTINCTLY different view of St. Louis style pizza. I actually had to open the box from Imo's the first time I ordered from them to make sure there was anything in it. I am not a fan of their pizza. It's commonly referred to (by non-native St. Louisans) as "snot on a cracker". The crust is super-thin, the sauce is more of a ketchup base (or tastes like it) and provel is some nasty cheese.
However, if I'm not mistaken, Kraft foods owns the patent on "Provel". It is a VERY regional pie, and I've never experienced it outside the greater metro area of St. Louis. I considered it to be a horrible rip-off (weight of finished product).
However, the national chains did have to stop and take notice and modify their menu to include this regional pizza. I saw one of the chains (I THINK it was Pizza Hut) making one, and they pulled out what looked like a tortilla for the crust.
Oddly enough, the "Chicago cut" (using squares instead of slices), is employed as part of the St. Louis style. Since I only eat deep dish and stuffed pizzas, I have never seen a Chicago cut on a Chicago pizza
In short, IMHO, Provel is not a cheese I'd want to duplicate. I also don't consider St. Louis style pizza to be of the same credibile types as Chicago and New York styles which have permiated most of the country.
No offense to the original poster here, just that I don't see St. Louis style pizza being worth trying to duplicate. Don't worry though, I feel the same way about California style, which I haven't even brought myself to sample.
To add a positive note to all of this, while I lived in St. Louis, an Imo's driver was robbed. He hit both robbers and killed one with a .22. Everyone in the pizza biz rejoiced at the news (though some more silently than others).