From your first post I'll assume that you are not making the lowers, you're buying Title I lowers from another vendor and having them marked with your information so that you can make them into an NFA firearm as an 07/C2. If so:
- Buy the Title I lowers and log them in to your A&D book, (or have them drop-shipped directly to save on shipping), then log them out to the other FFL.
- The other FFL engraves your name, city, and state on the Title I lowers.
- You get the Title I lowers back and log them into your manufacturing log.
- Build gun(s), updating your manufacturing log as needed during the manufacturing process.
- File Form 2(s) as guns are finished if they are Title II guns.
The only reason for a marking variance is if you were starting with an 80% (or less) receiver that the other FFL is finishing out for you and marking with your information.