guarantee if the pan is pretty smashed up especially in the center then thats the problem. A buddies s13 motor had no oil pressure just like yours, oil light flickered but stayed on for the most part, He thought the pump was bad so he started pulling it apart and had me do a complete gasket makeover on it including headgasket, oil pump, front main, and all the other ones on it. Put it back together and he put the lower pan on which i hadnt taken a look at and sure enough still no oil pressure (hmm i though) then i asked him what the lower pan looked like then looked under the car and said you idiot. haha there was your original probelem from the beginning. The pan was soo smashed up that there was an oval indent mark on the inside of the pan from a perfectly sealed pickup tube opening. Took the pan back off, hammered the pan back down and put it back up and whalla, perfect oil pressure. That motor ran like a champ too.
Neways definelty make sure your pan is all the way hammered out to where there is a nice curve sitting below the edges of the pan not bowed upwards. That will take car of the problem.
Oh and i doubt the oilers were clogged as yes that would increase oil pressure not decrease. Im sure your timing chain and everything is making noise not just the lifters. Also if the noise is loud enough your lifters arent getting oil either. Since you have it off i would replace the oil pump anyways especially if it ran dry because of another reason, Replace it and hammer the pan out and you will be good to go i guarantee it.