Be very careful...
"Restricted and prohibited firearms can be registered to the business. " Not so for prohibs if you ever want to resell, Dave

Once a prohibited handgun or firearm is transferred into a business inventory, it can never again be privately owned.
You may be able to hold one for sale on consignment, store it , or work on it under a clause that states that for the purposes of working in a gun shop/store, an employee is deemed to have the next category of licence bla bla bla.
Or something very close to that wording
It would be interesting actually to see just what it is that you (as a licensed gunsmith) can and can't do with these prohib firearms! I do know that even though I am licenced for 12(5) among others, this last year they removed the portion of my Business Licence that used to allow me to "test and demonstrate"/. Bummer! As of now, we can not store them, repair them, or test them, only possess for resale on behalf of a licenced owner. What next?
As for the original topic, I had known of no training requirements for Gunsmiths, at least not by the federal guys.
Gunnar
www.armco-guns.com