Connect an accessory oil pressure gauge, find out what the oil pressure REALLY is. The '88--'89 oil pressure sending units for the dash gauge are known high-failure items.
www.automotiveforums.com/vbulletin/showthread.php?t=1136624
Oil Pressure Sending Unit--TBI V-8 dash gauge C/K
www.automotiveforums.com
Some folks wind up with plugged filters---the media crushes down and becomes impassible. (Lookin' at you, Fram) But there are reports of crappy filters from other companies, too.
Even Wix is offshoring to China and Poland and God-knows-where, now.
HOW do you know there's no oil to the "top end"? Have you pulled the valve covers and run the engine?