Replacing clutch shaft...

So I managed to strip the threads on the sprocket side of the clutch shaft yesterday, so I started tearing it down for replacement. It's a good thing I stripped the gear puller trying to remove the clutch hub though, as it gave me time to do some research and find out the case doesn't have to be split to replace the shaft.
I removed it by tapping from the sprocket side, clutch hub and all. Stripped it all down and I need a new shaft and at least one bearing. The shield popped out and I'd rather replace it, as it's only a couple bucks.
Anyway, the shaft itself. Mine has halfmoon keys, and the slots do not extend into the threaded portions of the shaft. Now, I don't know if it's just the pictures, but both Pistonbikes and Gasbike show a shaft that looks like it takes a flat key with rounded ends and the slots extend into the threaded portion. I'm going to guess that these keys are not full length and I can still tighten a nut as needed.

Questions:
Do I spend the $6 on the flat keys.
Since I'm running a 415h chain, do I splurge on the 415 sprocket that Gasbikes has?
Since this area is separate from the engine itself, I assume shielded bearings like stock are OK. IOW, Rubber sealed is unnecessary.
I should be able to use the stock washers and nuts to secure the hub and sprocket, right?

So it used the half moon keys?
The picture they show for the whole assembly shows the same style key as the pic I posted above. Apparently I need to call them, because I'm also worried that if it is this other style that uses the flat key, are they the same width so my clutch hub and sprocket fit.

Look closer at the pics I posted and you'll see what I'm talking about. I'm not talking about the spring at all. I'm referencing the two slots near the ends. My shaft and apparently the one you have use half moons for the hub and sprocket. The pic I posted of the replacement shaft shows a different style of slot, which uses flat keys instead.