[ChrisS]

NCRS (where I been a member for several years) accepts restamped engines for judging so long as they are struck "factory typical". I, however, believe that when a VIN appears on a block, that it is implied that it is the original engine that the car left the factory with.
A large percentage of state vehicle laws that I have researched forbid the stamping of a VIN by an individual on any drivetrain/body part. Some, like Illinois, allow it if done in the presence of the proper state authority. In Illinois it is still a violation of the motor vehicle law to even posses "rosette" rivets.