At a glance, to me it looks like a '73 SG Standard. I think in '74 they moved the bridge pickup closer to the bridge but it could be early '74. The bigsby is a factory Gibson installed one that is Gibson branded. But is the arm on it broken?
I'd go along with Steve D on this one; I had a natural- not walnut one from 1974, but without the Bigsby. It passed to another collection which has since been dispersed. One of the two 1973 Specials in my collection had the 'Gibson' Bigsby; both these guitars went to France in exchange for a 1974 Flying V so as to complete a mid-sixty's suite of natural coloured Gibsons: T'bird, Firebird, Explorer and the V.
Now somewhat dated, Gibson SGs by John Bulli was nevertheless a good reference book.
Roger in the South Lakes, UK.
That's a gorgeous '76 SG there. The white with ebony really pops!
Back to the original question, In '73 / early '74 the fretboards were bound and rosewood. After that they went to unbound ebony like yours. It's not the best photo but I think the guitar ronniejackjones posted has rosewood and binding. That was another clue I didn't mention to date it around '73/early '74. But you know with that pic it's hard to tell. It could have unbound ebony, a pickup right by the bridge and be from '74-'77ish. Better picture immensely helpful to nail it down.
The SG Standard was introduced in 1961, slotting above the SG Special and below the SG Custom. It has been one of the longest-lasting variants of the SG, only shortly being replaced by the SG Deluxe from mid-1971 to mid-1972. As they transitioned back from the Deluxe, there were some models with...