From what I'm hearing (mind you I'm no mixer or pro, just a music lover):
- Tape saturation and lots of compression
The beginning of the song ducks so much when the drums come in! Love it!
- "Bad" mixing (no modern separation of sounds)
The drums are super-compressed but you can't really hear them. The clarity comes from the added percussion. The guitar is super dry, the bass is just all bass, the organ is there but it too is buried.
- Plate reverb/room reverb
Lovely dark reverb on those vocals.
- Mono
Well obviously!
- Crazy good vocals that are upfront and have a melody you can hum +lots of harmonies
This is what I miss in most of todays music. And I'm not talking about modern pop that's on top of the charts on Spotify. I'm talking about music! It needs more harmonies and melodies you can actually sing in the shower. So yeah, you need those!
+ Dynamic song structure. I think this is where it all begins! A good song! That's under 3 minutes!
My 2cents.
ps. Like I said I'm no mixer but I read about this Abbey Road EQ trick you can do on vocals, or rather the reverb. Not sure if you know this allready but here:
https://westlakepro.com/abbey-road-reverb-trick/