On the other hand, given the description, it may well be an early SP1 upper.
The difference between the Air Force surplus pieces and the commercial SP1 jobs is solely in the size of the front hinge hole. The Air Force surp units will fit a current lower unaltered. The SP1 has a larger hole in front, and will require an adapter sleeve to make it fit.
Also, there should be some markings on the barrel, ahead of the front sight base. It will at least be stamped C MP. That's the early model unplated version. It may be stamped C MP C, or C MP B. The first is a barrel with a chromed chamber. The "B" stamped barrels have a fully chromed bore. The very lastest versions were stamped C MP CHROME BORE, but given that the thing has a three prong suppressor, it would almost certainly be too early a produced piece for that.