The problem is that you can never proof your rifle left the Obendorf factory with a mismatched bayonet lug made in the Borsigwalde factory. It could have been changed out at any time, even yesterday. It is what it is, you have an all matching K98k, except the bayonet lug. That is not uncommon, parts brake, certainly on a battle rifle.
Does it have any modern German proofmarks described on this page: http://www.beschussamt.de/ ? Can't you post some pictures?