Man I would have a hard time doing that to a gun that my grandpa gave me. Not to mention you will have a short action cartridge on a long action receiver. Plus opening up the bolt face and mods to the stock and magazine will need to be done. It will be more expensive than buying a new rifle. This is just my opinion but I say keep the old 270 that way it is and if you are dead set on the 270wsm then buy a tikka or savage. If you are really needing a rifle for 400+ yard shooting I would consider a different round. Something with that will have bullets with higher b.c. Like the 6.5 mm's, big 7mm's, heavy .30 calibers, or even a .338.