Pulled the head today to inspect it. My biggest fear was pulling it, finding a bent valve and no root cause, with a solution, but no cause and no way to prevent it again.
Well it looks like I didn't have to worry about that.
I pull the head, see the valve stuck open and lo and behold...
That is an M6 bolt wedged between the valve and head. The valve isn't bent, the seat isn't chewed up, and there's just a cosmetic imprint on the piston.
Odds are I'm going to get a new valve and just throw it in there. The old one may be ok, but I haven't been able to get the bolt out, and think I might have to destroy the valve in the process.
Here's where it get's funny. The ports in the head are taped off. I taped them off as soon as I pulled the blower. I was scratching my head as to how the fuck it could get in there before I taped it.
Then it hit me. When I pulled the blower, I remembered one bolt was missing, and the rest were kind of loose, which was right after I picked it up from the fabricator. He also had an 01 Cobra in the shop and another he was mocking up with mine that was running a different intake manifold. I highly suspect that he must have yanked the blower to mock up whatever he needed, put it back on, and never noticed that bolt got stuck in there.
I suppose I'll count myself lucky that I didn't send it up there with a running motor, because it would have been much, much more expensive. Not to mention if I didn't find this now, it could have wrecked a very expensive motor. As it stands I'm out some time, a valve, and $35 for a head gasket. Not a big deal.
Only question that lingers is if I should pull the other head and inspect it while I'm at it, which would be another $35 for head gaskets.