Mosin... I never bothered which way it went, so one day in discussion with fellow alcoholic backyard mechanics, the general opinion was that oilway on top was best.
This is what we reasoned.
Oilway to the bottom means very little oil to the top surface of the shaft and also less bearing surface at the underside, where you need it, but possibly more oilflow to the loaded area.
Oilway to the top gives a wide oil film which can enter the low load side of the shaft/rocker, and the remaining oil in the oilway stays there by gravity to flow to the radial groove at each end.
You could argue that the reduced shaft diameter where the oil holes are forms a more than adequate oilway, and as the radial groove at each end coincides with the rocker oil hole feeding oil to the underside of the rocker arm and hence the valves, it really does not matter anyway.
The pictures in parts books and service sheets illustrate the oilway on the side of the shaft. So, top, side or bottom, I suppose you take your choice, even then you can bet it will move round when you tighten the acorn nut.
Swarfy.