Ah yes, that's the ACE "ARFX" stock as opposed to the regular skeleton stock for the modular folding block adapter.
I'll be drilling and tapping the rear trunion of my PAP when the eStamp clears; it shouldn't be too difficult. I'll be using the Manticore triangle folder along with a Storwerkz folding adapter screwed into the rear trunion. There's a slight angle to the trunion, but since I'll be using irons this should be just fine. It's the easiest way to get the stock type I want without having to remove rivets, gut the trunions and refinish the gun. That, and I just can't get behind the looks of the USMachinegun adapter pieces.
If my drilling and tapping goes awry, I'll simply use a small backing plate, washers and nuts to secure the bolts to the trunion. Using high quality bolts and refraining from butt-stroking anyone, I think it's gonna be just fine.