I think the neck is a (Gibson?) Mini humbucker - I don't think it is a standard on an SG - unless Gibson made one of their "crackhead specials" - look at their luthiers co_ckups page for these. Pretty sure the bridge pu is a Seymour Duncan-or copy- as there were not many replacement pickups made when your ax was being customised.
From the wiring I'd guess that both were replaced (and a little badly if i may say) as you've got room for a humbucker in the bridge i'd say you had room for one in the neck and it's been routed wider...but this could be wrong as the SG special came with p90s about the same size ...so id like to ask
lalimacefolle
Lordathestrings
Jon Broderick
et al, about this as they know their Gibsons.
Ps I think Gibsons serial number info is really confusing.. anyone??
Accuracy,you say? hmm interesting concept..