Interesting topic.
I've read the factory letter for #500,001 and it too is a .308 though the rec'r dates to 1947. The LBC indicates manufacture 1960. And is Rentzschke engraved.
The above mentioned letter says Rentzschke worked at Savage/Chicopee ~1956 - 60 and did engraving similar to what we call "A" engraving and did some special rifles such as the One Millionth 99.
Examples of Rentzschke engraving for Savage