A couple of years ago I visited the Accurate Reloading BBS quite a bit. I have the Kodiak Mk IV in .45-70 also and was thinking of rechambering to .450 NE #2. There were several folks on that BBS that had done that. Some did not have to re-regulate but others did so I know that it can be done. My rifle will group like yours with .45-70 and I have not re-chambered. I still want a .450 NE #2 though.

Best regards,
David