I wouldn't doubt a bolt head would be changed out to tighten up head space but many rifles left the armory with No.3 bolt heads. I couldn't venture a guess as to the number, but in this case, a Savage marked No.3 bolt head being found that indexed correctly AND head spaced correctly? A No.3 bolt head is difficult enough to find to begin with...what are the odds of finding a Savage marked one that was right on the first go?
AS to the rear strap on the forend....I have seen this type of fitment before. I don't know if it is something done from new or a "re shape" of some kind to fit a new pin. It also appears to be sanded along with the contour of the wood.