Crab
Lot's of different parts (Westland Sea King vs Sikorsky H-3 or S-61) including the major assemblies you mentioned.
The MRB difference is down to the folding head nature of the Sea King versus the fixed head of the S-61. Rotor diameter is the same, blade length different. Or at least that's what I remember about the Carson blades (designed originally for the S-61)
Nick