I recently purchased a GSG-5P from a fellow INGO member for a great deal. After shooting it a few times I have decided I definitely want to put a stock on it and make it an SBR. As I undertand it, the first thing that I do is send in my Form 1 paperwork. Once I receive it back from the ATF I am free to go ahead and put a stock on it as it is now registered as an SBR. My question is at what point in the process do I have to get it engraved? What are the requirements as far as what I have to have engraved on it?