This has been a useful discussion: it reminded me that I still had to tighten the bolts on the newly installed 164 engine mounts on my B20. After doing so - a task made a little bit more difficult due to the hexagonal plates on top - I remembered John Parker's observation that 164 mounts raise the center of gravity. I wondered by how much and got out my calipers. After having it heard said so often that B30 mounts are heftier than the 140 type -- the reason why I got them in the first place -- I was quite surprised to find that the dimensions are identical,i.e., 1 9/16" high and 2 9/16" diameter. Only the upper metal plate is larger, but it doesn't increase the height of the mount. In fact, the 140 mount appears to have a little more rubber in it. Perhaps the larger plate makes it sturdier, and the rubber is firmer?
Bob S.