Look behind the left side cover (under the seat) to see if there is a voltage regulator present. If it's there and it appears to be connected you have the original 28A stator. If there's just a 50-60A fuse holder there then the upgrade has been done. Another way to tell is to look behind the small gray panel next to your left foot. If you see a smooth solid looking case bolted to the back of the engine, that's the 28A unit. If you see a vented case, looking like a miniature car alternator, that's the 40A upgrade.