These are made to work with the Romanian underfolder stocks and will not work with the Polish or Yugo sets. There are a few places that sold the Romanian "G" front end with the Yugo rear trunnion and underfolder stock that are totally different.
The flats are made from 4130 annealed steel and come with rails that have mag stabilizers on both sides like the originals. The right side rail even has the bump on the rail to keep the hammer centered in the receiver.
These only work with the Romanian Trunion.