I bet that it is in fact a factory instrument, and that it left the factory in 1971-2 era using left-over parts. The 2 would help to confirm at least to me that Gibson did this as a standard practice (ala the 1962 Explorers). This may have started out as a double neck, or they had a couple of crapped up axes in the SG and EB0 wreck room. This is my pet theory which dovetails into Gibson using the basses as the training wheels work for new guys (Jules - how are those Kalamazoo interviews coming along?). "Hmmm, how can we make money off this salvage?" Presto - double neck. A black finish would cover up some sins there too, like how they started using sparkling burgundy to fix ES's. It would not be too far off to think it was original, although it could be a refin and with a price tag as unrealistic as that it could be a fake. With prices like those, if it ever sold, faking fantasy Gibsons could be worth your while if you had no conscience.
But again, times is tough for the vintage dealers. Especially those who cultivated the snob investment world and talked about these things like they were stamps or wine. Maybe they just overlooked, I dunno, almost EVERYTHING.
