Welcome to the British-Genealogy forums gabs999
SwindonLibrary hasn't been on Brit-Gen for a couple of years but maybe you could contact them yourself. Here is their website and they have an email address.
You could also ask them if they have newspapers for the relevant time.
If you purchased your father's death certificate from the GRO here it would give you his cause of death. You can order online at the GRO here and these are the details you need.

Donald Stewart Gabriel
Death Age 26
Birth Date - 20 Oct 1943
Registration Date Dec 1969
Registration district Swindon Wiltshire
Volume 7c Page 2219

This is his birth registration
Donald S Gabriel
Mother's Maiden Surname - Walton
Date of Registration Dec 1/4 1943
Registration district - West Glamorgan, Glamorganshire
Volume Number -11a Page Number 1330

This looks like his parent's marriage
September 1/4 1942
registration district Swindon vol 5a page 110
As his parents may still be alive I am not allowed to post their names. However if you go to FreeBMD here and enter the surnames you will find the marriage and their names. They must have moved from Swindon after their marriage.
You can also use FreeBMD to see how many brothers and sisters your Dad has. Highlight births, put in Gabriel, mother's surname Walton, dates 1942 - 1970
Christina