Helidogger, why not have all the parts fitted that make up the certified airframe? I am not an expert on maintenance issues, but in all generality I would assume that the a/c with any part missing cannot be deemed airworthy.
I once had a kink in the skid, and the a/c was grounded until a new skid was fitted. Reason given was the the each skid (including their uncompromised structural integrity that may be affected by the kink) forms part of the crashworthy undercarriage, where each part is presumed to absorb its share of the impact energy in a hard landing.
Resonance in high hover: Have you already tried blade tracking?