Anyone know how the triangle side folders are installed on a stamped receiver AK? Does one have to modify the reciver to fit them? Or do they just drop in?

http://www.k-varcorp.com/stock3.html

its advertised as the paratrooper stock

Yes,

The receiver has to be modified to support the triangle side folder.

The front of the receiver has a slot cut on the left side to support the spring loaded "hook" mechanism that holds the stock in the folded position.

The rear of the receiver has to be cut and modified to support the folding mechanism of the stock.

If you want the Triangle Side Folder "look" without the cost of modifying your weapon, then I recommend you go with the FSE Triangle "Fixed" Stock system.

www.rpbusa.com/ak.html

KF