The flywheel won't fit over the high output (650 watt) stator, so you must upgrade the flywheel.
The high output stator requires a larger rectifier, so you must upgrade the rectifier.
The high output stator has cooling thru the crankshaft, so you must upgrade the crank, for the oil cooling.
Not as simple as swapping out the stator. I'm pretty sure they wouldn't quit making the 420 watt stator, and require everyone with a 420 watt stator that goes bad to spend thousands of dollars upgrading all those parts, just because their stator went out. They made the 420 watt stator as late as 2014, no way they quit making replacement parts for machines as new as that.