Those old 6 Cyl engine got their oil through a passageway that came up along side of a head bolt ( the centre one I think ) to the rocker shaft. In the old days it was a common thing to take the head bolt out and clean the sludge out of the passageway. If it ran long enough like that you may have a problem with the rocker ball and pushrod seats as they would wear from lack of luberication.

Bob