The problem with converting a normal shotgun is going to be pressure. You can push pressures up to the .458 WinMag range if you use the Ruger Mk.1 load data. That will utterly destroy a shotgun.
That's why my .45-70 conversion project is using a PSL bolt and trunion, as they are rated for the 50,000 CUP pressure of the 7.62x54R. Other than a slightly greater bolt thrust due to the larger base of the .45-70, the hardware should support even the heaviest loads. I'm talking 500 grain projectiles!