audio commentary-unfilmed script

I'm trying to find an unfilmed script of the Phantom of the opera that was spoken of in the audio commentary.

It starts at about the point where Claudin has just killed Biancarolli and her maid and Garron is seen running after him.

I think it said that a man named William Lipscomb wrote the script. They were going to get Boris Karloff to play the Phantom, and Cesar Romero to play Raoul.

I try to look it up, but I don't get anywhere.

Thanks if you can help!