I have no idea what the 9AM1232 relates to.
The type C relates to the exact size of the bore and indicates you should use the corresponding type D pistons.
Yes,.. type C cylinders use type D pistons.

I agree with Andy that the heads are the same across R5k and R6k models.
Having said that,.. there appears to be 2 types of head that both work fine. See the very bottom of this page.
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...