The original copyright owner has the rights to decal designs from the past. However, if someone were to reproduce them, I seriously doubt the copyright holders (if they still exist) would bring an infringement suit unless they were still in business as one of the big time players.
To the artist that recreates the artwork and makes something usable, they should sell what they make to recover the costs. It's a hell of a lot of work and expense, and I doubt you could recover the costs unless you could sell 100 sets.
Been there done that. Go to an established painter who can get many decals, or Cyclart who makes their own.
By thew way, I have no problem with modern, computer technology. Its wonderful!
Ted Williams, starving graphic designer