| The engine will go in fine but you will have to re-plumb the clutch slave cylinder as it will be on the left hand side of the engine.
The 900 has a 5.5" wheel with a slightly different sprocket carrier from the 600 although they are interchangeable. ( I have a wheel and carrier if you need one!)
If you need to use the 5mm spacers from the 600 on the front and top engine mounts, make sure that they are on the right hand side of the motor otherwise the chain may rub the tyre, especially if you use a 180 section tyre.
If you can find an early 750 or 900 ally swing arm they are a bit stiffer than the steel 600 one.
Good luck | 
paynep
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