hippie,

The 110 to 90 is not a direct swap.The 110 has a longer stroke crank.The 110 crank will need to be machined to accept the 90 alternator rotor as its an inner rotor type.
The 90 cases will need to be machined to accept the larger 110 cylinder.The cam chain,tensioner,exhaust,intake,ignition etc are all differant.Lots of work for a small gain.

The noise you hear when you kill the engine is the clutch spinning to a stop.Thats normal,however some engines do it,some dont.

Tim