Thanks for the input.
I took the valve cover off Sunday night and checked the valves. All four are within spec. They are at the tight end of spec, but they are in spec. I may check them again this winter just to see if anything has changed, but that's apparently not the cause of the sound.
I could believe that it's a clattery timing chain. That would definitely match what I'm hearing, along with a bit more vibration. The only thing I find strange is that I'm sure it has changed from how it used to be. However, I'm not about to tear down an engine just due to a little vibration. If the engine wants to be torn down that badly it will let me know over time.
As a note for those who may be looking at checking their valves soon, here are some tips.
- It's pretty much like any other twin cam thumper.
- the valve cover must come out the right side, not the left.
- you don't have to drain all the coolant, just from the upper radiator hoses.
- removing the lower radiator bolt helps get it out of the way.
- you don't have to remove the throttle body like the book says either
Everything in mine looked really nice and shiny with not scarring or pitting on the lobes. I've seen other engines with no more milage that did not look as new. This is certainly a good sign for the longevity and specified maintenance interval.