In the Berlin production whenever he was alone with the gargoyles, he spoke clearly. When he sang, he sang clearly. With the other characters (not in his head), he had a speech impediment.
Regarding makeup/costume.....the makeup was expensive and consisted of glued on rubber parts molded to each actor playing the part similar to the Phantom in Phantom of the Opera. The hunch parts were also molded to each actor who played the part......the actors did not share hunches.