Here’s my take on the tune. The key is in C# so it’s capoed at the first fret and played in C. This could be one of those recording tricks discussed earlier here where the engineers speeded up the tape to brighten the sound. Let’s ignore that and just discuss this in the key of C. The starting chord sounds like a C7(flat 5). From the 5th string thru the 1st the notes are: C, E, Bflat, Eflat, E. (It’s a C7 chord with the E-flat added at the 2nd string.) The first string E can be played or not. Dave is lifting that chord and leaving all strings open on the up beats and then resolving the dissonance into a standard C chord before he starts singing.
The song is a straight C,F, G format, but its filled in a lot. I suspect Bob might have capoed up and played in A and Nick’s tenor could be in there too. That gives the tune a rich filled-out sound when added to Dave’s 12-string. Hope that’s helpful. – All the best, Meade