Somethin else that's been known to happen to big blocks....the oil pump bodies can crack and actually break right where the shaft housing meets the rotor housing. It's cast as all one piece from the factory, but I've seen both old and new pumps fail there. That will make oil pressure drop and could make it drop gradually over time as the crack gets worse and oil is pumped through it right back into the crankcase. This is why I magnaflux EVERY pump I use. Also considering I rebuild all my pumps to save money as well. I have found some cracked ones, too.
