A little tear down update. I finally tore the top end off today. I do remember having quite a bit of valve train noise before, and I think I figured out why. The intake lifter on cyl 4 was grinding itself to death and starting to take the cam lobe with it. I could only push the pushrod seat with finger pressure on a couple lifters, and 2 were visible collapsed, there was scoring on a couple that I couldn't feel.
2 front bank and 1 rear bank exhaust valves were yellow with sulphur build up
Flaky carbon buildup on all the pistons
Cylinder bore scoring in cyl 3 that I could feel.
Here'* the bad lifter pics, it'* pretty deep: