Jack, maybe print out some of the ATF guidance on manufacturing.
I like the one where it says that if you buy a mil-surp rifle, install and new stock on it and offer it for sale, you are manufacturing.
When I applied for my home based FFL in CT years ago my zoning officer got a bit nervous when she saw I was applying for a manufacturers FFL. I explained that what I was doing was "light assembly" and it eliminated the problem. Its a definition thing. ATF defines things as manufacturing that aren't really manufacturing.
If I'm an 07 and I buy a fully built lower as a receiver, and pin a fully built upper to it and offer it for sale, I'm manufacturing per the ATF.