You don't have any problems.
It seems it's the version Helicobloc from Verney-Carron, manufactured during 1950th, proofed with 1100kg/cm = 15635psi,
right barrel ***** = cylinder, no choke
left barrel *** = 1/2 choke.
1 1/4 oz lead shot 2,5mm (No.7), 1350fps in a 12 x 70mm cardridge is a normal load to hunt pheasants,I do it every year in autumn.
With steel shot you will have problems with the barrels.