Carrie could potentially be a great play. I'm not sure it can work as a musical. But it showed such potential in a few of the songs (Evening Prayers, Unsuspecting Hearts, ect.)!
They didn't work anything out. By all accounts, the show stayed pretty much the same when it arrived stateside. I think the key to making Carrie work would be to set it in the conventional, small-town setting that the book and movie used. I don't know who was smoking what when they came up with the design concept for the musical.