If going for a 250 twin cafe racer bike I'd go with the newer cb250 nighthawk as a starting point over a 250n - they are much lighter engines I'd think, deffinately look lighter / smaller gearbox. Reasonably economical. Not that common as a 400 though if at all. I have the begginings of a 125 project in the shed using a cm125 engine in a ns125r chasis, should handle well and judging by my rebel 125 with same engine it should go well enough for me - the rebel easily did 70 until recently - compression now well down and struggles to get past 50. Poor 125 twins seem to need rebore at 25,000 -30,000 miles. Personally I think half the charm of owning a cafe racer is to build it yourself. A 550/4 cafe can be a nice looking bike and plenty of them to get insiration from on this forum. I know of a firm who've built featherbed frames to accomadate the 550/4 lump for something that bit different.
