Well,what the BATF might do is a question. In all honesty unless you did something to attract serious legal attention there would be little to worry about.
But, then the BATF made a big deal about Thompson Centers 410 Contender barrels. I always wanted to machine a copy of a Stevens 311 receiver, take a set of barrels and put shallow 1 in 50 ft "rifling' in them and have a need pistol. But, no that would be an illegal short shotgun or a pistol with a bore over 50 cal and illegal. Now the Shockwave deals are all over the place. So, can I now make my short 12 gauge, no shoulder stock, 10" barrel double "pistol"? It sure appears so.
In the past even for some time after 1968 gunsmiths could restamp the serial number in a new location and move the original. Now that is a no without express permission. All the guns previously gone would still be legal.
In other words they go one way then another. One agent might interpret the law one way and another different.
My brother had a old Parker double stolen from him. Kids that stole it sawed it off short. Got caught. They got a minor spanking and if the local law even told the BATF nothing was done about the felony sawed off.
If the BATF prosecute for this type of thing they could easily browse and find some on Gun Broker and the like to charge with this. They don't. As said they got better things to do.