I know this is weird replying to a question I made a year and a half ago, but I have found some evidence to suggest that both houses may have actually been in Soundstage 22 instead of Soundstage 23 like so many websites say it was. First, if you look at the maps for both 1995 and 1996, the label for Universal's House of Horrors and Universal's House of Horrors are both clearly on top of Soundstage 22. Second, look at this press release from 1995, which says that Universal's House of Horror was in Soundstage 22. https://parkrumors.com/archive/95sys.php
Also, the Universal House/Museum of Horror houses from 1995-1998 were all reportedly very similar, so I would not be surprised if they kept some of the props and rooms in the same Soundstage between events. If anyone has some information on this can you please let me know? Sorry for the inconvenience.