Dirty Oil- PCV Fail?

[SofaKing]

I drained the engine oil and collected a sample of strange looking, non-magnetic, black particulate matter from the drain plug. I drove the truck 12 miles and drained a sample of oil and it was black. I drained it again and drove it 6 miles and it was very dark. I have not driven it since the 4th refill due to time.

I have a 1936, 21 stud engine and driveline from a humpbackcar. It was assembled 2 years ago, has less than 5000 miles. It was thoroughly cleaned by machine and with bore brushes by me prior to assembly. It is stock with the exception of a pcv system. No oil filter. I am using 10W40 Castrol. My first suspicion for the source of the particulates is the clutch housing through the labyrinth rear seal due to the pcv. My pcv system has 15” hg steady vacuum available at idle from a 1” spacer under the carb. The pcv valve is located at the front of themanifold. The oil pan road draft is blocked-off. I put a vac/press gauge into the manifold pcv valve port and the crankcase pressure is ambient, abrupt throttle changes don’t cause the needle to move.

I checked, primitively, the clutch housing airflow with a3/16” wide strip of paper. The result isthat the paper, if held ¼” away from the top vent, oscillates to and away from the vent. Get it slightly closer and itis drawn into the vent suggesting a slight low pressure area inside the clutch housing. I did not plug the drain holeon the bottom or attempt to seal anything, it is in as-driven condition.

I have blocked off my pcv system and will drive it a whileto see if it makes any difference. I amnot real happy about this since the draft tube is blocked but will only be fora few months.
I mention this because it may be useful info to others considering a similar pcv set-up and I am looking for suggestions for otherpossible sources of the oil contamination, or testing methods. This is my first flathead so I have no basis for comparison.

The pictures show the concentrated particulates, dirty oilafter 6 miles, and the paper sticking to the clutch housing vent.