I think you'll find there are some internal gearbox ratio differences between the 5th and the 6th. The crank is obviously different (gear vs chain sprocket for the cams) but AFAIK the bore and stroke are the same (so maybe rods and pistons?), and I assume the lower crankcase is too. I suspect the alternators are different. I know at least one person has swapped a 5th gen engine into the 6th frame so I presume the engne mounts are the same.
So aside from the crank, upper case/cylinders, heads, gearbox, alternator...its all the same? Probably doesn't leave much.