Blackie plays his Gibson SG Standard on all Hard-Ons and Nunchukka Superfly projects. Seems like it's his all-round #1 guitar. He very kindly gave me some more detailed info on the battleworn axe.
Apparently it dates from 1980 (a '61 reissue SG Standard) - and he got it cheap because the headstock was broken (!) Blackie fitted a brass nut to replace the original, and had the pickups waxed so they didn't feedback as much. He also noted that the neck has been broken three times - but still sounds amazing.
The (white) bridge pickup mount is also clearly a replacement.