I think this may be your John's death registration (he seems to be the closest fit to your John):
Name: John Davies
Estimated birth year: abt 1816
Registration Year: 1887
Registration Quarter: Apr-May-Jun
Age at Death: 71
Registration district: Bedwellty
Inferred County: Monmouthshire
Ebbw Vale was part of Bedwellty registration district until 1894, as far as I can see.
I believe the General Register Office is putting some certificates on line for a reduced cost - not actual certificates, but show all the important information. It might be worth having a look.