The fixed and folding stocks both fit the same receiver. The stocks bolt into the receiver using the same hole.
I'm seriously considering using my tax refund on one of the OOW receivers. It's a LOT for a receiver, but it does include all the compliance parts. And it's not a common rifle to see in the U.S.
Assembly is just like an AK. Press barrel, check headspace, pin barrel, then assemble other parts and shoot.