After breaking in the cam on my 460 rebuild, I spent some time tuning the carb and ignition. Took a few drives, probably 10 miles total and everything was ok, still idling a bit rich. Started it up today to do a bit more tuning, and found that cylinders 5 and 6 have a good bit of oil on the plugs and leaking from the slip joints on the crites headers. So, it's either the rings (new and cylinders bored)' head gasket or valve seals. The heads are the only part I did not personally rebuild. They are aluminum edelbrocks I bought used but looked lightly used. My guess is it's likely the valve seals, but before I start tearing it all part again, I wanted to get some input. Would a comp check tell me much? If the oil rings are somehow bad, which seems unlikely anyway, the comp test won't help. Any other thoughts or diagnostics before I tear off a head?