Every engineer has his habits/tricks. Take the bass - wrap an rca mike in a towel and stuff it under the bridge, place mike xxa six inches in front of the bridge, place mike xxb near the f hole, etc, etc. You can do this stuff for any instrument. They could (and did) eq each instrument to their taste. To remix any session properly requires an understanding of the techniques used, the reason for them and the best way to play them back. Many of these choices were made to compensate for the way the tapes would be interpreted by mastering engineers of the day - and their goals. Not an easy thing to understand if you haven't been working in this area.