Thanks,
I'm not excactly sure, but I just brought it to the bike shop to have it installed and the kid sworking there said that it did not fit because the chain ring was touching the chain stay. They said that the S300 was track crank and I needed a specific SS MTB crank instead.
The S300 uses a GXP bb if that matters.
Specifically, they mentioned the width between the chainstays on a MTB are wider than a road bike, so it needs to be wider to clear the chainstays.

I'm not sure what you mean by spidle, do you mean the axel that is attached to the drive side crank arm? I think that is permenantly attached.