Roll-marking doesn't take all that much to accomplish, and it's done with a die, not by engraving - 'just' like the factory would have done.
Back when Winchester was selling off a 'lot' of their stuff, I knew a guy who bought a number of their barrel dies for rare, or hard-to-find calibers, along with a number of other interesting things.
For several years, if you were looking for a brand-new pre-'64 barrel for your Model 70 in .22 Hornet, or something more exotic - he'd tell you he 'knew a guy' and could find you one - then he'd fixture it up on a new barrel blank, and suddenly you'd be writing a check.
He was a whiz with re-welding and re-machining cut, demilitarized receivers of .45s, Garands and Carbines as well.
The dealer in question didn't do his nefarious 'work' personally - someone did it for him - but that someone's name has never 'really' come up.