Thanks to a tip off from drakula63 (I posed the question to him about the chord) I decided to finally join this fine forum.
Regarding the topic i.e. what's the Maroc 7 chord? I have spent some time listening to it in depth and also ran the whole thing past a music teacher friend of mine who is also a composer. If you're wondering which chord I'm on about, it's around 24 seconds in, Hank isn't playing and you only hear Bruce play the chord between Hank's phrases.
We also looked at the ebay sheet music link above and listened to the track for the best part of 2 hours. Tragic I know, but it has to be done.
The chord in the sheet music is Bbm6 (B flat minor six), which is ALMOST correct. We both believe the chord in question is actually a Bbdim7 (B flat fiminished 7th). Both my music teacher friend and I both agreed we can hear an E note at the top of the chord, and thus we believe it to be the following chord voicing on the guitar, where you play 4 notes only:
E X (don't play low E string)
A X (don't play A string)
D 8th fret
G 6th fret
B 8th fret
E open string
Breakdown:
8th fret D string is B flat
6th fret G string is C# (or Db, minor third from B flat)
8th fret B string is G (G is minor third from E)
open E string (E is minor third from C#)
I'd play it like this:
This we believe makes it a B flat diminished 7th chord - the E is open string and it's tricky to hear it but we're both sure it's there. You can hear a full piano version of this chord here:
https://www.scales-chords.com/chord/piano/Bbdim7The Bbm6 in the sheet music would be correct if an E was added on top, so like I say, I think it's almost correct.
I noticed the guy in the Shads Tribute playing a straight Bbm bar chord which totally works and is much easier to play, but I believe that to be totally correct you'll probably need to go with the voicing shown here.
Of course, this is only my opinion and I could be wrong. If there is a better sounding chord than this one out, I'd love to know what it is.
Incidentally I love Maroc 7 and it's a crying shame there is no live version of this from The Shads.