[loudist]

I would imagine that it was 3 track back then.
1. Whole backing track
2. Lead vocal, lead guitar (if the solo doesn't step on the vocal or visa versa.)
3. Backing vocals along with piano or percussion when backing isn't singing, you have to analyse what leaves when the backing vocal are in.
One must remember that they made recordings very quickly back in those days. I'll bet it didn't take them 3 hours to record that song, mix included.

If you have a 2 track tape recorder, consider recording the music backing track mixed live and compressed onto one track mono. Do a few takes so you have editing possabilities. After recording and editing the tape, transfer that to adat as a safety, but continue to work on tape using the other track for lead vocal. When that is done then transfer both tracks to adat again but on a different portion of the adat tape and finish the 3rd track overdubs.
I don't agree that compressors weren't in every studio, possibly they compressed the buss to the tape instead of every single input.
Hitting tape really hard in those days didn't sound all that great because of the tape formulations of the day, and then there is the issue of adjacent track crosstalk across the heads with super hot recorded magnetic flux.