Info & Value for Savage 99 w/ mannlicher forend in 303sav caliber & SN 258xxx

There's a Savage 99 in 303 savage caliber with the full mannlicher forend listed in the local trading paper. I called and the guy is looking to trade it. The serial number is 258xxx, but neither he or I know much about it ot it's value. Was thmannlicher forend a factory option or an add-on? Anybody have any insight for me?

Yes savage made a full stocked military rifle, but that serial number would be too late for a factory production. Sounds like a custom of some description.