Sadly these reports were rarely retained - the police side were weeded after 7 years (in some forces up to 10 years) and the PF's side a little longer. Often the RCE is the most information you will find or the newspaper reports you have already seen.
The procedure would have been that as the death happened in a public place that the police submitted a report to the PF. Acting on that information and as it is suggested that the family GP did not issue a death certificate (you say PF signed death certificate) there may have been a post mortem to establish cause of death.
Taking this information the PF had a number of options
1. If death was suspicious - have the enquiry continued
2. if not suspicious and cause of death attributed to natural causes - have the death certificate issued (info to Registrar who would create the RCE)
3. Continue Inquiry by interviewing witnesses to establish 1 0r 2 above
4. Establish cause for a Fatal Accident Inquiry.
It's a pity really that these reports were not retained as a full Sudden Death Report sometimes contained a summary of several generations of the family.