In 2007 Orion came out with the CRF .21 motor with this sort of crank machining. The B321, Wasp and the 7 port had these cuts as well. May have been a few more. The on-road motors had this as well.

The CRF RS, does not have these, but instead the rear of the crank has 4 additional ports drilled angled into the Crank Center.