well it has a 2 finger slider, a megareg from Nitroduck and it looks like it was forgotten about since the turn of the century.
the PTP detent could be a retro fit, as the early WGP bodies didn't have detents stock, till 97ish, or you had someone drill it.
its a P block, so it falls right in the 97-98 era but again, it could be a milled p-block, as only Belsales and STOs had them stock.
it could be a house cocker or someone wanting a bunch of parts. its a legit gun and if you get it cheap enough, a good buy.