Ok, I think I have it, Sec 6.4 last paragraph.
If the applicant on the Form 1 lacks the skill, ability, and/or equipment to manufacture the NFA firearm,
the applicant, after receipt of the approved Form 1, can have the firearm created or modified at a
premises other than shown on the approved Form 1 as long as the creation or modification was done
under the direct oversight of the applicant, thus having the applicant retain custody and control of the
firearm. If the location is outside the applicant’s State and the firearm being made is a short barreled
rifle, short barreled shotgun, destructive device, or an unserviceable machinegun which is being
reactivated, the applicant will also need to request permission to transport the firearm interstate as
required by 27 CFR 478.28.
Does that sound about right?