For reference, the rocker arm shafts have a notch on one end and it does go to the bottom as gf7cuda said. When facing the engine from the side, the notch goes down and to the left. In other words, the driver side has the notch at the front of the engine and the passenger side has the notch at the rear of the engine. This also orients the oiling hole in the shaft to lubricate the rocker arm properly.
NOTE: You also want to check the narrow and wide holddown retainers for the rocker arm attachment bolts are in the correct locations. If not, your rocker arms will not be centered on the valve stems and the pushrods may be "angled". It is hard to get this wrong but who knows? Might as well check it.
Here are the diagrams.
This diagram shows the rocker arm shaft holddown bolts. Each bolt has a retainer under it. The ends and center bolt get the narrow holddown retainers (location 1, 3, & 5). The wider retainers are at locations 2 & 4.
Narrow end retainer with notch at bottom of shaft and the retainers with bolts.