How many km's has your bike travelled? My Classic 350 has got progressively smoother as the km's increased, and I really don't notice vibrations at all now through the bars or the pegs at open road speeds in the 90 - 110 range (I'm currently at 16,000). My understanding is that the 350 is slightly shorter geared than the 500, and I'm not aware of a smaller sprocket to gear the bike down any lower. If the bar vibes are too much to tolerate then go with the foam grips suggested by Wildbill. Have you checked all engine to frame mounts? My biggest comfort issue was the original seat now replaced by a Lycette saddle, and that has made a huge difference on long rides.