[notmytarga]

Another avenue to explore is to have the oil analyzed. Aluminum/Magnesium engine parts are not going to spit out metallic/magnetic debris. Horrible part wear might give metallic bits that may or may not be attracted to magnetic probes.
The next oil change will be more clear if it is assembly lube. Mine looked much the same. In Wayne's rebuild book it describes the 20 min oil change as necessary to clear out those metallic bits - several discussions over the years have asserted that it is the appearance of the lithium based assembly lube that it seen at that point - not metal. Wayne's description of expecting metal would really be a catastrophic problem. I would think that the 20 min oil change would be ideal for just about any rebuild rather than after certain work - just to flush out the non-oil lubricants and sealant remnants.