P14
P14's make great big bores but you probably are better to sell and purchase what you want. If the rifle has been sporterized, stock, receiver, scope mount etc. your conversion costs will be less. Probably the most cost efficient big bore conversion is 458 Winchester- P14 bolt face is correct, receiver does not require modification for "short magnums", magazine will work with a new P17 follower, barrel and installation is the major cost. Barrel should be obtainable for $300-$400, maybe more, maybe less. Also the 458 can easily be downloaded to 45/70 velocities. Good luck.