Check oil pressure - with a gauge either in the switch hole or into the main oil gallery (remove a gallery plug, drill & tap 1/8 NPT, install a NPT brass plug afterward).
Oil to the head comes up through the barrels in galleries at either end. The control orifices are between the barrels and the main case. Once in the head, I'm not too sure how oil gets out to the cam bearings but it may just go to the outboard bearing and eventually lube the inboard ones by filling the cam trough. The cam lubes from that trough, oil splashing/spraying from the cam and tappets gets everywhere and provides tappet and guide lubrication. You can't really see into the trough from the tappet covers, but should see that the cam is wet and see oil being flung around when the engine is running.
If you have decent oil pressure but no flow to the valvegear, you will have to pull the head and barrels to check the orifice valves. These do get clogged by any crud that gets into the engine oil past the filter. Using silicon sealant in the engine is bad for that, bits extruded from sealing surfaces when torqued break off and block small passages in the galleries... those orifices for example. Poor maintenance that allows the oil filter to get really clogged will activate the filter bypass built into the filter bolt - that allows unfiltered oil into the main gallery.
If your oil pressure is super low above idle you can have enough to trip the pressure switch (~5psi) but that's not enough to reliably oil the engine. You may have assembled the oil pump or its pressure bypass incorrectly?
