Bob,
I'm going to jump in here on the valve clatter. Random thoughts:

Have you tried to change to a lighter or heavier oil? If it is clatter that is cam or lifter pump-down related the oil change may change the noise and it would isolate the problem to that area specifically. They are hydralic bucket tappets so the oil change would effect them too of they are tuckered out (hard to believe at 60K though). Have you pulled a cam cover to see if the cam is OK (not scored or otherwise beat-up). As long as you have the cam cover off, measure the valve to tapped gap (heel of the lobe to tappet).

Getting away from the valves, I remember the first time I heard the saturated circuit style fuel injectors I thought the valves were bad. They click like crazy and you might be hearing that.

Have you tried the old "yard stick to the ear" trick to isolate the where the clatter is really coming from? Get a yard stick and put place it on different areas of the engine and then to your ear. You'll hear many things this way and maybe you can find out if the clatter is coming from the cams or from another area nearby.

An accessory belt will click when it gets old but it is a different type of click of "clatter". Different in that the timing of it is different than the valve train. Less rapid. Timing belts: not that I have ever heard.

As for the codes, if this car was sitting with bad gas in it. You probably need a fuel injector service. The car is going to need the injectors serviced at 80K anyway so why not now? Adding stuff (Techron or whatever) to your tank will not clean a fuel injector that is dirty they must be removed. If you have lean injectors the CPU will try and compensate and you could be getting into a "lean-rich" loop. Here in the Seattle area we have a place called "Dr. Injector". They clean them for about $35.00 a pop and they also flow check them before and after. They also do it by mail if need be. Look for something similar in your area. They come out real easy, take less than a day to get cleaned and are a good D.I.Y. project.

That's about all I can think of of right now. Hope this helps. Good luck.