No cop will pull you over and say anything about your motor. I would just tell them to prove it IS stolen. Just because somebody decides they want to do something to their own property doesn't mean they stole it. You won't have to prove its not stolen, they will have to prove it is....

But the real key to the shaved block thing is, the code on the bottom of the block. If they removed that, chances are it is stolen, lol........