I installed mine as they came in the box, no soaking in oil or pre-filling stuff. A simple test to see if they are pre-filled (I think) is to press on the "button" in the center that contacts the valve stem. It should be very firm, if not rock-hard. Some of my old/worn lifters would leak down and the button would easily push in. I just coated the new ones with fresh Mobil-1 and dropped them in, then poured more Mobil-1 over the cam lobes after re-installing everything.
Regards,