Bob,
I think you need to know what year engine it is. There are two ways for the oil reach the center oiler on the rocker assembly. One method had a small tube hidden under the side cover. The little fitting going into the block was prone to plugging.
The later version utilized an internal route through "the magic head bolt..or not". I am going to leave the rest of the explanation to others, as this subject seems to be controversial, at best.
Stuart.
