I finally had a chance to test side rail with r/s PSO1 scope. It doesn't fit. Rail construction is slightly different from r/s or Guarder rails. So if you want to use r/s optics or RDS than you will have to replace the rail.
Edit, apparently PO scope (civi version of PSO1) fits ICS AK. I just found some pics of the gun with PO scope on it. Doesn't make any sence to me since both scopes are made for the same side rail as far as I know.