Welcome Dmcgee,
They wont fit a rifle barrel to a shotgun (SB-1) frame. The rifle (SB-2) frames are machined from a block of steel that has been hardened to a much stronger frame to prevent stretching. The shotgun (SB-1) frame is machined from a casting then case hardened to a degree, but not to the degree of the rifle frame.
Read this from H&R/NEF's barrel program and it should answer most of your questions.
Barrel Accessory Program
Additional barrels may be added to firearms of our manufacture since 1987 only, with a serial number that begins with N or H. We do not install additional barrels on any other manufacturer’s firearms.
Additional barrels are available as additional barrels only. We will not exchange barrels for existing barrels on shotguns and rifles, as it will change the model.
Rifle frames may be fitted with additional rifle, shotgun, and muzzleloader barrels.
Shotgun frames may be fitted with additional shotgun and muzzleloader barrels only.
We do not sell additional barrels outright. All barrels must be factory fitted.
We do not sell barrel blanks or do custom calibers.
In order to obtain an additional barrel(s), the stock, forend and frame (receiver) must be sent to us so they may be properly hand-fitted to the barrel, to be sure they are correctly head-spaced and proof-tested.