To keep the long story short, I had my car down to bare block, crank and cylinders (kept in the car). Reworked heads, new oil pump, radiator, thermostat, water pump, gaskets, etc...

Car is finally back together and I cranked it up last night. As the engine starts to warm up, low oil light comes on. I unplugged the sending unit and the engine light came on so the unit is ok. There is also a "clapping" sound coming from one of the heads which I think is coming from the unpumped lifters due to "no oil".

So the question is, "Was I supposed to somehow prime the oil pump after installation?"