Don't know about Abba and Deep Purple but I just remembered that Dave Mason had the proverbial "cup of coffee" with Fleetwood Mac in 1993 or so. One more guitar notch on the band's bedpost.
Also, the band does have some interesting (and unexpected) fans. Radiohead has been pretty vocal (and did that USC marching band tribute at the Grammy's on the 30th anniversary of the "Tusk" release) and Matthew Sweet - guitar connoisseur extrordinaire - once referred to LB in his liner notes as "a rock god with the power of Zeuss in his fingertips").
Marty