I think we can both agree it's one of the finest bass sounds ever recorded, and I'd also add that I agree with you that it's not like his later metal sound, and really much closer to his gut sound at the time. Probably he was still using basically the same setup and technique as with gut, and also I don't think those are Spirocores, maybe something else. Not to mention he was still hearing the sound the same way at that point, I would imagine.
John Clayton has that bass now and of course has it set up his way with Obligatos, but you can hear some of that quality in it.
If the sound is a combination of;
Bass
Strings
Setup
Hands
Recording
Then, I'd say it has 2 of the 5 still with it. Same bass and John's got a lot of Mr. Brown's hands in him. I would like to think that I would have recognized that bass from the sound, but I recognized it visually when he took it out of the case. It's distinct, beautiful instrument.
And yes, that record is a clinic on great walking bass lines.
Troy