Yep ) It's the MUNY version of the show, and is actually the original theatrical version - it predates the RSC version which is almost identical to the movie. The MUNY version is less technically demanding (the RSC version is quite complex technically) and is closer to the original L. Frank Baum book. There's information and synopses etc etc on the Tams-Witmark site (www.tams-witmark.com); I did this version at school but it was a fair while ago and I've since been involved with the RSC version so my memory of it is a bit sketchy. From what I remember, Glinda is never named, she's just the Sorceress of the North; Toto doesn't come into it at all, there's no Poppy Field sequence and things happen in a different order from the film. I also seem to remember there being something about a bridge which swings round (pushed by the Wicked Witch of the West) every time Dorothy and the three companions walk over it. Plus the Wizard takes Dorothy back to Kansas in a rocket rather than going up in a balloon basket leaving her behind. Some of the songs from the movie are missing (King of the Forest and the openings to the three If I Only songs aren't there either, mind you they're not in the film, only in the RSC version anyway) and there's an extra song for Dorothy called Evening Star. Plus, as you say, the Wicked Witch doesn't melt, she gets thrown into the cauldron and shrinks.
I have no idea where you could find the script, but if you Google MUNY Wizard of Oz or something along those lines you might have some luck. Break a leg at auditions!