I hear it as tape all the way, sounds better than it ever has before, but listening in headphones....the EQing makes it seem like it's not in true mono. Might just be my ears, but one of the channels seems louder and has more treble than the other. Monoing out one of the channels makes it sound a lot better.
I haven't done any intensive listening or testing, but if it was cut from the mono master, it might have been played back on a two-track (stereo) deck, which would create subtle stereo artifacts.
For you computer audio types, you can split the stereo track into 2 mono tracks, reverse the phase on one, then combine them into one mono track to find out if this is the case.
To me, it sounds like a vinyl rip ... but apparently it's not. But the whole set seems to have some kind of analog-emulation (distortion) plug-in or something across the tracks.