So if I've got you: The lower guide fails and causes slop in the chain which the tensioner is unable to adjust. So the loose chain slips and wham-o, top end Cap'n Crunch.

For my current examination if the tensioner is keeping the chain tight then the lower guide is still intact.

You recommend only the three guides up top. No tensioner? How often do you replace the tensioner?

Also on a slightly related topic a few posts have suggested replacing the oil rails. Are those the plastic rails that run just above the injectors? Should they be replaced also? I thought I was looking for the rail above the cam bearings.
I agree with you on the chain. I think I am looking at less than a degree of stretch. I don't think I need to change that out.

Steve you have been so helpful and put some of my fears to rest.