Yes sir you can use the Laser II Rudder on a Laser, but you most likely will not be allowed to use it in races as it is not class legal. Besides the little chip and the grime on the Rudder, it's great!
Also, I went ahead and posted the pictures in the original message for all to see.
I don't have a Laser 2 rudder at hand right now, but just measuring from the pictures, the pintle-to-pintle distance is more than 20 mm longer in the Laser 2 rudder head. Also, the tiller is about 40 mm higher from the bottom fitting. Even if the pintles are the same exact fitting, it would be a very bad fit on a Laser. I'm beginning to think that the Laser 2 rudder fittings were totally changed (pintles on the transom/gudgeons on the rudder head) just so no one would even try to put a rudder on the wrong boat.
The Laser 2 rudder blade doesn't fit the Laser rudder head, either. They're simply two different designs.
But the bottom line is that it would be a waste to use a Laser 2 rudder blade for anything else than a Laser 2 - it's the only L2 spare that appears to be out of stock, worldwide, and there's no guarantee that Crompton would build any new ones, ever. Even with the chip, that rudder is worth more than USD 150.