Would it work on a WASR that came with a fixed wood stock?

I think those stocks require the removal of the rear block and installing the correct block for the stock, as well as installing the latch up front.

If you want a plug and play stock, the E. German or Romanian wire side folders will pop right in.  I have a Romy side folder on my SAR1.  Those stocks just use the same mounting holes as the wood stock does, although those folders use a machine screw to screw to fasten in the Romy side folder.

Its hard but can be done, first you will have to weld the original stock "trunnion" holes shut, grind them down flush. Then fit the bulgarian "trunnion" to the receiver, you have to cut the rec. at a 6 degree angle when fitting the "trunnion". Here comes the hard part, theres two ways of doing the front slot for the folder catch, since you're converting to a bulagrian folder your problem is the front trunnion is already riveted in, it can be done without removing the barrel and the trunnion but its a real PITA, i did it so it can be done, but if i knew how long it was going to take me i would have removed the barrel, trunnion and the rivets just to do the slot. cutting the slot is not the problem, installing the spring that puts tennsion on the catch properlly is the problem but it can be done, it took me about an hour to install the spring.  First locate where the slot goes (there are templates on "pookies" website) cut the slot and drill the hole on the bottom of the rec. then fit the catch and the spring.  in the following pictures you can see by the first pic i got ahead of myself and installed the barrel before i cut the slot for the stock catch, in the second pic you can see that i did get the catch in but it took time to get the spring right, theres not much room between the trunnion and the bottom of the rec. so it takes time and a lot of cigarettes to get done without bashing the gun with a sledge hammer, lol. This rifle is bulgarian but gives you an idea of what it looks like installed. Good luck. McM