Is the topend on the 400ex and 350x the same? I no the 400 has more cc's but are they interchangble and how does the 400 get more ccd bore stoke? And are the bottom ends similar? the 350 is a 6 speed I was wondering if you could put a 350x bottom end on a 400ex with the 400 topend has anyone dont this and would it be worth it?