The oil pressure is also from the rod bearings, not just the cam bearings. If a rod is loose, the oil pressure will drop. And it will have that knock. If it was me, I would just replace all the bearings and gaskets. 120 K miles isn't very much, there are guys in here with 300 K. Mine has 159 K with all original bearings and stuff, its just fine.
***--- Wrecking Crew member ---***
"I've prolly been around longer than you think"