The very first 3 bass notes…that’s not an electric bass is it? It almost sounds brassy.
And right after those, on the sustained treble note…what makes that sound?
Can’t fingure it out 
I think that’s a tuba, followed by a flute and guitar.
Tenor or baritone sax?
There’s some percussion behind it, probably timpani. My girlfriend and I are thinking the melody is being carried by tuba, maybe bassoon or double bassoon. Several other instruments start playing on the downbeat (third note), so it gets complex quickly.
My ears hear this. The blatt of a tuba backed up by some timpani hits…
I don’t hear the guitar. That high note is muted trumpet doubled by flute.
I’m going with a Baritone Sax too.
As a former bari sax player, I have to agree with “bari sax”…it has that feel. It’s not brassy enough for tuba, I don’t think. It sounds much more woodwind.
OK, I get the muted trumpet part now; still can’t hear flute though. The bass ‘blats’ seem too punchy for tuba, but who knows what they can do in a studio. I was even wondering if there could have been some synthesizer involved, although this was around 1970 so it would have been with something like the old Moog-type equipment.
Listen to the fourth note (the one that’s held for a couple seconds.) There’s a tinny, brassy part (the muted trumpets) and there’s an airy, whistly part to it (the flute.) They play at the same time at about the same volume.