A lot of Stihl and Husky mufflers, especially on older models, have no baffle. The 066 is a special case though, as is the 046 because they generate a lot of vibration that would lead an open muffler to cracking. The 064 saws first came with open mufflers and I have about ten or so with big cracks through the back after a few months of use. As far as spacers go, Stihl actually makes a spacer which allows you to put a newer 036 muffler on an 034 or a newer 066 muffler on an older 064. They do seem to help a little as far as scavening goes, but I'd put the gains in the 1 or 2% category, not much at all. Whoever did the work in those pictures did an excellent job.