You wont need the grooms father's name to get the marraige cert - in fact you will be getting the cert to find the grooms father's name!
You will just need the year, quarter, registration distr and ref no, and I believe I have them all on the other thread.
Hopefully the marriage cert will give Johns father's name and occupation. If you are lucky it will give an age for John, and addresses - but anything will be a help at this stage.