If that Guyot was mine and it was made after WWI and the wall thicknesses at the end of those chambers was 100/1000ths or thicker I wouldn't hesitate to shoot factory 2-3/4" cartridges packed with 2-1/2 DE of powder and 1oz of shot. Of course, if I blew my fingers off it would be my own damn fault.
Lengthening the forcing cones has merit. There is a warning from Gough Thomas/GT Garwood about long forcing cones and fiber wads and shot balling. But as long as you shoot modern plastic wads through those lengthened forcing cones there should be no problem. I still wouldn't shoot any factory loads over 2-1/2 DE and 1oz of shot through it though.
In his paragraphs about shot balling Garwood also mentioned that many Continental guns (like France, Belgium, Germany, but not England) left the maker with long forcing cones. Which means you might already have long forcing cones.
You probably won't live long enough to see the effect on the gun's value of lengthened forcing cones or a lengthened chamber or making the gun out of proof.
Presuming that Alaskans have a lot of time on their hands in November, December, and January, you could reload a lifetime supply of 2-1/2" length 16 gauge shells in one winter.
I assume you have had the chambers measured and they have not been lengthened already.
Last edited by AmarilloMike; 06/12/15 10:45 AM.