A local musician asked me to make him something that would do this, and it really seems to be about that last 5% of "raspberry" at the end of some of the notes and some other unique flavors. I figure some of it is the finger picking (& some gentle palm muting?), and it's possible it was a really small, crappy amp that was being mic'd too. I'm sure all of this has been discussed to death! I kinda love the mystery of it, and I certainly haven't built anything for the guy yet.
The Bosstone is not a bad guess, but it's not necessarily because of the "built into the guitar" SITS thing; it sounds like Greenbaum's was truly built
into the guitar while the Bosstone was a little box that connected directly to it. Any fuzz circuit of the time could have been crammed in there.
The Bosstone never had a germanium version as far as I know, but there were LOTS of iterations, including two rather different versions from Alhambra alone - and that was
before the Pasadena version and most ubiquitous Nashville ones. The very first one has tropical fish caps and a tantalum as well. The second Alhambra version was more like a Fuzzrite tone-wise, and I think there's a chance the SITS circuit might be closer to that - Fuzzrites can get pretty assy, after all. In a good way.

Mosrite was in California too, so it's possible NG's guitar tech knew Ed Sanner! Ya never know.
It's been a minute since I went down the Bosstone rabbit hole, but I'm a hardcore Spirit freak so I looked into them way before I was building anything.
Here's one of the threads I had bookmarked from DAM, might be interesting. Post #33
here has more timeline pics.
This has a quick demo of the trebly Alhambra V2, transitional Pasadena, and classic Nashville versions. There's also an
isolated version of the song that helps you hear what's goin' on.