I’m not sure of your meaning and I assume you are referring to a G/K43. If you have a G/K43 receiver then it either has a integral scope rail that is in the receiver forging OR you have a receiver that has had the rail milled off. I have both types in my modest collection; the typical railed G/K43 and the far less common variant with the milled off scope rail. To my knowledge you don’t simply “add” a rail....but I might be misunderstanding your question. If a G41, well, that’s a whole new topic.
It's a G43. Well it's a DUV44 reciever so I wonder if someone sliced it at one point? Or maybe it never had one. It's a A block DUV44
Yeah it looks alot like that will post pictures soon. Why did they mill it off do you know