Ok, here are a couple of new pieces to the puzzle. I forgot to mention that last year, my rocker arm shaft literally broke in two while running down the interstate. It broke off at the rear pedestal and temporarily disabled #6 exhaust valve. I replaced it with a used one from a 216 engine I had sitting around since it seems to be the same part. I took off the entire rocker assembly today and measured the used and new shaft (the front half that didn't break) with a micrometer. The used shaft has up to .002" wear on it but the rockers don't seem sloppy at all. The engine was doing its noisy valve thing before the rocker arm shaft broke and has done it since. This was only 1300 miles ago but seems like an eternity since it was last year.
I noticed today that I have a bluestreak DX-70 condenser on this engine instead of the DX-90 that I have on my other 235 engines so I changed it out. But given the info to forget about the blue spark thing, perhaps that has no practical effect.
As for valve adjustment, I used your companion cylinder method, Hotrod, only I used the opening of the points in the distributor to find TDC for each cylinder. This time I tightened 3/4 turn from pushrod snug tension. All the rockers are oiling properly. Unfortunately, I was pretty sloppy at finding TDC last time, and had one valve that was overtightened to 2 1/2 turns. That was probably the exhaust valve that sucked paper at the tailpipe. That has since cleared up as well as the excessive exhaust noise volume, but as you say, Denny, the damage may have already been done.
