Most, if not all of the songs on this record come from 1", 8-track tape. So, much like the Sly Stone GH (which also had a few songs from 8-track) drums were recorded mono. So, it is very much a limitation of the multitracks. It really seems to me that Columbia Records had a "16-track or better" Edict to avoid mixes like this. Inevitably, some did get put out, like Sly.
However, in my miniscule mixing experience, I've found if you only have one track of drums, if you're lucky and have one track of percussion - put the percussion in the adjacent channel so you have a stereo rhythm section. This works really well in the rears and I did just this exactly on my 4-channel remix of Marvin Gaye's "I Heard it through the Grapevine". If you have a bass, piano and a guitar, you place those across the front with bass up the middle and you have an 8-track mix that really explores the 4-channel space without leaving any dead space in any channel. Often times when I mix, I put bass in all 4-channels to really flesh out the mix.
My biggest gripe about this Laura Nyro mix (and it's a very personal gripe) is that I would've mixed it my way with drums/percussion in the back, vocals and bass front center; ancillaries wherever. I don't like where on "Eli" piano and tambourine share the channel. To me, that's conflicting. In my mind, if instruments must share a channel, each instrument should occupy it's own frequency range. If you have bass in one channel, compliment it with horns, acoustic guitar or percussion. Don't fill one channel with a bunch of all mid-rangey instruments because then it becomes the dominant channel. I can understand why this mix was possibly rejected.
Like I said, that's a very personal gripe. It's all in my head, really.
Aside from that, I'm like a puppy at Halloween with this release. Not enough Scotch-Guard in the world will protect the front room carpet. An unreleased Quad mix finally seeing the light of day after almost 50 years? Vindication at last!!
Speaking of rumoured, unreleased possibly EPIC Quad mixes.... Sly Stone's "There's a Riot Goin' On". It was announced and made it to a bunch of record jackets as "Coming Soon".. Please oh, please look for that one!