Yes. The only real difference is the stock pivot pin size. The ones on the poly side folder are a bit bigger. Don't quote me, but I think the larger end is 4.5 mm. It is stepped down to I think 4 mm. To intall on the metal side folder trunion, you need to open the holes for the pin a bit. A reamer works goog, just chas what is there now.
The Russian Polymer stock will fit on a Bulgi rear trunnion but you have to make a new henge pin and drill out the top loop of the henge on the rear trunnion. Just make sure you drill ONLY the top loop of the henge. It's not a very hard mod. to do. I used a small grade 8 bolt. I cut the head and threads off then put in my drill press and held a file on each side until I got the larger part of the henge pin to 5.5 mm the smaller or bottom end (stepped down part) of the pin I made the same size as the Bulgi. pin. It only took about 1/2 an hour to make. Then I put several heavy coats of Navel Jelly on the raw metal of the new pin and inside of the upper henge loop to give them a nice phosphate coating and prevent rust and it gives it a correct look. The Russian pin is 5.5mm and the Bulgi is 4.5mm. I hope this helps.