Here's the final update on this thread, then it's back to business on the truck build thread. I did indeed have coking on the valves. I took the head back into the machine shop to get positive seals installed, it should be back next week. They also noted it was running wildly pig rich, which I agree with. I'm going to downsize the carb to a freshly rebuilt Holley 390, and I got a wideband sensor so I can see what's up with the tune. Between bad timing, running too rich, and what-all else, this go-round should turn out better.