Without seeing the gun I would say no on shooting 3" shells. But if it has a large enough ejection port you can shoot 3" shells but no bigger then that. And if the barrel is thick enough to be reamed out and threaded it can have multiple choke installed I have done several. But would need to find out how thick the steel is at the muzzle to see if it can be done. Also you would need to be sure the barrel is the same all way around. I have come across some guns made same year barrel was same inside and outside but was out of round (more metal on one side) those can not be done Have a good Gunsmith check barrel thickness and see if same thickness all way round. I hope this helps Please be sure to give me a positive feed back. Let me know if you need any more help.