turns out I didn't need the spacers after all, but a google search found many people recommending pvc spacers, no mention of problems. Remember though, adding preload just adds x amount of spring pressure, constant at all levels of suspension compression. So it makes the biggest % difference near minimum compression, and the least difference bottomed (so it isn't a good mod to prevent bottoming). A heavier spring rate is multipled throughout the travel, so the % increase (not the amount of increase) is the same anywhere in the travel. What is your goal with changing springs?
well, regarding the 10 wt. I had special ordered it, so I went ahead and put it in, we'll see how it works. The valving probably was pretty mucked up, lots of really black looking oil came out of these forks. I flushed oil thru the works until it came out clear, but wasn't able to take apart the cartridges.