Looking for help on a model 70 bolt problem. I recently acquired a used custom made rifle on a Model 70 action. serial # on receiver 77,XXX. It is marked 375 Magnum on barrel. Problem is the bolt will not close on the cartridge. Bolt appears to be a standard bolt and not a magnum, and therefor will not close on the rim. Guy I bought it from later admitted that he inherited two rifles from his granddad and stored them with bolts out. Probable bolt swap with no chance of retrieving the original. Rifle is not a Joe-Bob alteration, it was built by Al Biesen, unfortunately no longer available for consultation. I have since purchased a magnum bolt, which I thought was pre-64, but it will not go into the action. It has an extra width on one lug with an "anti bind" grove in it which blocks it from entering the action, which I believe makes it a post 64 "classic" bolt. My questions: 1) Can I use the standard bolt and enlarge the face opening to accept the 375 base? 2) Can I machine off the anti bind piece and use the post 64 "classic" bolt. I know I need to have headspace checked. Other suggestions? Cal