According to IMDB (though not always accurate), Hell House was mono "Westrix Recording System". During this period before the later part of the 70s, most Fox titles (with some exceptions) were recorded in mono and includes bigger titles such as the remaining Apes movies and Rocky Horror Picture Show (of which both received stereo and 5.1 mixes much later on). During the VHS goldmine years, it was common for later releases of mono titles to be "digitally remastered" with a stereotized 2.0 mix (sometimes labeled stereo surround) which is in most cases, delayed l/r channels with reverb. This carried on to the DVD years for mainly 30s and 60s titles along with more obscure 70s/80s titles.
However, around the height of the DVD glory days, Fox did invest in completely new and redone mixes for popular titles and some action/sci-fi/horror that only had mono mixes. Many of these utilize whatever original dialog and music/SFX stems have survived (or in some cases, aren't too damaged to use), though most of not all do take liberties with ether adding or changing lines and SFX/musical cues. Many of these were 5.1, although there are ones encoded in Dolby Surround 2.0 (almost always a downmix of a multichannel remix if it were mono originally) and others were strangely encoded 4.0 discrete (L-R-C-Mono Surround).
What makes that even more perplexing is that Fox did 2.0 and 4.0 discrete encodes for 1950s-60s mag track recorded CinemaScope titles and a couple 80s/90s titles. I remember seeing a DTS DVD of Point Break that not only had a 5.1 DTS remix, but also sported a DD 4.1 Surround track that probably a discrete version the theatrical Dolby Stereo L-R-C-Mono Surround with an LFE track strangely added (possibly tacked on from the 5.1 mix), and a 2.0 Surround mix that is most likely the Dolby Stereo LRCS "unaltered" but matrixed to 2 channel.