Boy! Where do you start! Obviously, this ain't American. There is a place for a speed governor and/or a rear distributor, but what all those holes do, I couldn't tell you. The three lowest holes go into the oil passages. I was really intrigued with lowest one which is the capped one down on the side of the bell housing. It lined up perfectly with the outlet on the oil pump and seemed to be an easy route into a nearly full flow oil filter system. I imagine that a passageway runs from this passageway into the passageways above it just like an American block, so that vertical line would have to be plugged, but I wonder if you could just tap a snugly fitting sleeve into the lower passageway to block the oil going upward. That way you wouldn't have to do any drilling or tapping and wouldn't have to worry about metal shavings going where they could do the most harm. I didn't have the presence of mind to see if the vertical passage was already tapped for a plug, but that would be way too easy. The assembled engines apparently have the same poor partial flow oil filtering system that is found on American flatheads.