Most likely the name you read as "Cesare Giadanelli" is in fact Cesare Giovanelli who is the founder and maestro of the Bottega Cesare Giovanelli, an engraving school and atelier in Gardone, Val Trompia, Brescia, Italy.
The Bottega Giovanelli does a good deal of outwork for various gunmakers in Brescia,including Beretta. Along with hand engraving, they also do the roll die impressed decoration on production model Berettas.
BCG's usual marking is found alongside the triggers and reads "Inc. Bottega Cesare Giovanelli." The Inc. is an abbreviation for incisore, which is Italian for engraver.
The gun in question seems to have a variation of the usual marking. From what you wrote, the gun may have been engraved for a friend of Maestro Giovanelli.
Given the value and unique aspects of the gun in question, I am surprised that your friend doesn't know more about the provenance of the gun as it is rather unusual for such a fine shotgun to find its way into the hands of someone who knows little about it.
Regards,
CRB
