Modification question, would it be right

[Setter Man]

I would not do anything to alter the barrels, ever, especially barrels belonging to an English gun. It’s hard to find English guns that haven’t been messed with. Brits know how to take care of their guns and refinishing didn’t effect the value like it does with American guns, but any alteration of the barrels will reduce the value of a British gun.

Lengthening chambers will let you shoot 2-3/4” ammo, but at some point low pressure 2-1/2” shells will be available, but your barrels will still have been modified.

[mobirdhunter]

I agree and concur with what's been offered in response to your question. IF the gun is still in proof, opening the chambers will take the gun out of proof, and, as stated already, reduce its value. Also, the Brits removed lots of metal in making great handling guns and it is not uncommon to have barrel walls be in proof and be much thinner than what you might find in an American gun of the same vintage. Opening chambers and, especially, forcing cones, could be disastrous.

Good things come to he who waits.