Before you pull it back apart and start throwing cubic dollars and parts on it....why don't you rig up a mechanical gauge so you can see it while you drive. If you see the oil pressure drop when you get the noise...oil pump or oil delivery system. If the oil pressure doesn't drop...probably bad lifters. You may have a couple of lifters that have trash or something in them that causes them to leak down randomly.
When you had the oil pan off, did you check the pickup? If the factory nylon timing set is disintegrating the screen will have lots of debris on it. If it was clean, someone has already changed it more than likely.
When you had the oil pan off, did you check the pickup? If the factory nylon timing set is disintegrating the screen will have lots of debris on it. If it was clean, someone has already changed it more than likely.