This is what is bothering me.....loss of oil pressure would not seem to be the cause of the troughs. As said, look at everything up through the oil into the rockers. I am suspicious of something coming down from the rockers, or the valvetrain being jammed. We don't know if a PO had some retainer to guide clearance issues, messed up the cam bearings, threw in some straight pushrods and/or another cam, and sold it.
Yes 'evenly' is a word! LOL