It CAN be a major concern. The headspace should definitely be checked by a competent gunsmith to determine if it is correct. Mismatched serial numbers can cause serious problems. A good friend of mine once changed bolts in a 303 British. The bolt seemed to work fine. Upon firing the gun, it blew the bolt and action apart. He was very lucky all he received were a few minor scratches and a big scare. Most definitely HAVE IT CHECKED!!