Those highest notes happen too close to my ears.
   Hello DonMeixner, I have an aluminum whistle that sounds very different from the "tin" ones. It has a plastic mouthpiece and a cylindrical bore like my other whistles, so the tone change must come from the material, right?
Speaking of bore, a Clarke has a tapered bore, which would be difficult to fix if it was sat on. You'd need a metal or other hard piece the same taper as the whistle, so I don't have much hope for your injured Clarke, Mo the caller. If the bore is straight sided you can drive a dowel or similar object through the whistle and straighten it out pretty well.
My best to all,
SKP