Geoffers,
The 1984 CAP 491, HARP Report to which you refer doesn't seem to be available electronically; only CAP 641, Report of the Review of Helicopter Offshore Safety and Survival, published in 1995, which refers to it:
Report of the Review of Helicopter Offshore Safety and Survival,
or the AW presentation New Technologies in Rotorcraft Mechanical & Rotor Systems:
New Technologies in Rotorcraft Mechanical Rotor Systems
both of which also make for interesting reading with regard to ditching survivability and improved engineering concepts.
CAP 641 was updated in 2005 by:
Helicopter Ditching and Crashworthiness Research
The UK HSE also has some interesting on changing helicopter accident rates in the UK sector:
Helicopter safety
Sorry, that hasn't answered your question and is a bit of thread creep, but all are interesting documents in view of recent tragedies in the offshore helicopter world