I also think the harp you hear is an organ, but I don't think it's played by Bill!
Probably Nicky Hopkins, though I remember vaguely a rumour around that time that it is Steve Winwood.
Re.: Brian's guitar playing:
there's a book on the Stones by Palmer & Shanahan
page 143 a pic from Keith's cottage with Keith & Brian playing guitar, Jagger is watching; sup
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