This is a great question!
I know that AR15 (restricted on completed) lowers that are 60%-80% finished can be purchased without and PAL or RPAL as they have no serial and are not "technically" controlled in that state. Nor do they require a transfer.
The bottom line is does this type of manufacturing require him to be licensed at some level of government?
I would think yes, he needs to get licensed. DO I think he could do a couple on the side and not catch crap? Yes. But depending on how cheap these are he may WANT to get licensed. There is a pretty large demand for these due to the lower issues 180s suffer..
It makes one wonder at what state he could machine it to (say 95%) before it is considered a firearm and he needs to be licensed?