There is some big chunks in there. You say they are non magnetic whick would rule out oil pump gears cause they would be steel. Could be the pump housing. If you still have the oil send a sample away to get tested if you could be bothered. You are on the money with the valve stem seals, they cause smoke on start up. As lagwagon is saying, if you are going throught the trouble of doing the head, might as well inspect/repair the bottem end as well.