All L39A1's had the standard No4 butt fitted when built and issued to whatever unit! The butt fitted to the lower rifle (509) is a No8/Envoy/7.62 conv. butt fitted later in its life!
The Cadet Centar rifle were all engraved as such but there are very few around.
All the L39's were machined to take the 7.62mm Magazine, so that was just a case of take a mag off the shelf and fit it!