Hi Ian,
Glad to hear you had a good trip back to Dundee and Arbroath. Must have been nice after all that time.
Not sure how much you know, but here are some websites which will help you with your family research.
You have your great grandparents marriage certificate, so their parents should be named on that. That's your first step in going back - find their marriage and death certificates, which will give their parents and so on.
Probably the best thing to do is read the information on the undernoted websites, which will help you get back.
ScotlandsPeople give you online birth, marriage and death certificates for Statutory Registration, from 1855. They also let you search an index of Old Parochial Records, pre 1855. They also have online census'.
FamilySearch is the online index of the Mormon Church. If you go to the section IGI, this will let you search records' indexes, giving you names, dates and parents names, in the case of births. Unfortunately, there are no deaths as such, since pre 1855, not many deaths were actually recorded. It's not quite 100% accurate, but you will soon learn what's what!!!!!
The GROS website will give you lots of information which should help in your search.
Sorry, I am not very good at explaining things!!!!!! There are lots of "chatters" here who will give you help, so just post your queries.
Regards, Dorothy
http://www.gro-scotland.gov.uk/http://www.scotlandspeople.gov.uk/http://www.familysearch.org/