The Great-Kazoo is mostly correct.
If you make a NFA item from a manufactured Title 1 you must engrave the makers (trust) name and city and state on the barrel or frame or receiver. You use the manufacturers existing model, caliber, and serial number for the other markings. The serial number can only be on the receiver.
Page 35 in the ATF National Firearms Act Handbook covers this. The ATF National Firearms Act Handbook is an official from the horses mouth source of information. It is generally understandable. Chapter 6 is about making NFA stuff.
http://www.atf.gov/content/firearms/...s-act-handbook
I have never entered anything in 4h.
The barrel can be a handy place to engrave the makers information. You can change the barrel and sell it as a Title 1 without your markings on it.