left barrel is .040" a tight full choke
right barrel is .035" also a tigh full choke these guns were made for fibre wads so genenarlly shoot pretty tight with modern shells I have an Armi G Gamba that looks very much the same as your gun I opened the chokes up on it to .010" and .020" it is now much nicer to use
the 1.370 kg mark is the barrel weight a requirement at the time of proof if the barrels are wieghed and they are less than the stamped the gun is deemed out of proof (so adjusting chokes and forcing cones in Europe would render a gun out of proof)
18.3 is the barrel diameter the other number is the choke constriction 70 is the chamber lentgh not sure what the 20.3 is
check out your other post I posted some pictures of my Gambe for comparison
