I know you do not have to typically grind anything but rivets, I was just experimenting with the cheapest part.I am beginning to think you may have gotten a Brit MK II open bolt 303 browning kit or parts of one !! The lock frame ,cocking lever (Gunner your eyes are better than mine !!) how close the the lever slot in the bolt is to the right side , the sear cut in the bolt , the extractor and having to grind on the breech block all indicate something is not right !! Can you provide pic of all sides of each component ? Now know this i am not familiar with the MK II internals at all .....But you have something strange going on without a doubt !!