Good to see a fellow purple head, i got my license in 1972 and we wore out these four (and moire) 8 tracks, yes a couple last 8 tracks.
Deep Purple - Machine Head
Humble Pie - Smokin
Santana - Abraxus
Pink Floyd - Dark Side..
and many more, on and on
Let me tell ya, you havent lived if you never heard Santana - Abraxus quadraphonic on an 8 track.

Pure 100% channel seperation. Best thing I ever heard. Seriously. Very heady.

In Floyd's league.
heres a couple more obscure but very sweet cuts from those afore mentioned classic albums..
what a nice find, video to this song
this song we checked bass with, if the woofers didnt rattle.. good system