MachIVshooter:
The specific part of the CFR I cited was the same one that the ATF cited specifically in the handbook chapter I linked to that dealt with Form 1 engraving requirements.
So it seems like they're getting their Form 1 engraving requirements from the same place as the manufacturer requirements if I read it correctly.
If you read it carefully, and part 7.4, you'll see where the requirements for manufacturing a firearm and making a title II firearm from an existing firearm differ.
Licensed manufacturers must put the serial number on the receiver/frame, and the weapon must also be conspicuously marked on receiver or barrel with manufacturer location and caliber.
Unlicensed builders making personal weapons needn't mark them at all.
Unlicensed builders making title II weapons from scratch must mark them the same as a licensed manufacturer.
Unlicensed builders making title II weapons from existing serialized firearms must mark them with their name, trust name, or recognized abbreviation thereof, caliber, and city/state of the unlicensed builder as it is listed on the form 1. You
DO NOT have to assign a new serial number (and aren't supposed to), and you
DO NOT have to engrave your information on the serialized part of the frame or receiver. You
DO have to make sure that the relevant NFA engravings are present and easily visible on the weapon. Where something like an AR is concerned, your serialized lower is registered, but you can put the NFA markings on the upper or barrel if you like. But you will have to engrave any short upper or barrel you install on the registered lower when it becomes an SBR in doing to.