I did the valve adjustment on my 280SL on Saturday, and everything turned out fine, thanks to the Star article by George Murphy and the tips I received here.
I thought I would post two additional "tips" for mechanical novices like me, in hopes that they may help others who don't do these things every day. First, the valve adjustment specs are in millimeters, not inches (no wonder the valves all seemed too tight when I first checked them...). My feeler guages are were inches, and I had to go out and buy another set. I couldn't find a metric set, but the new set I bought contained two that were close to the metric specs (0.102 and 0.254 mm, as I recall). Second, be sure to remember to remove the wrench from the crank bolt after you're finished and before starting the engine! I did (fortunately), but broke out in a cold sweat when I pondered what might have happened if I had forgotten to do so.