Hello David, I assume that you are referring to your adoptive parents here, regarding the deaths? Condolences to you anyway.
From your story, I would say that it's very likely that your birth mother was a teenager and probably either of Irish parentage in England or sent here from Ireland give birth.
Your original name contains two surnames Beckenridge and Keehan. I would also say that there's a possibility that these could be your biological parents' names, with Keehan being an Irish surname, this may well be hers?
Your original birth certificate may give you much more to go on if ALL the information is on it. Chances are it may not all be there in cases such as yours but you may be pleasantly surprised. It's a gamble worth doing. You may find it contains some useful information like an address or better still, hopefully the name and occupation of your biological father?
I remember 1974 quite well as a teenager myself and the Marc Bolan poem is certainly something that only a ardent fan would know about, so I can say with at least small amount of confidence that your biological mother would be of a similar age to me or slightly younger. Currently I'm 67 years old.
Ancestry is a good idea too, I've been a member for years and you'll get many DNA matches to look at. This will also tell you how close you are genetically to the other matches. I suspect that there's a good chance that she's still alive and has gone on to marry and had other children. Plus other close relatives of hers or your biological fathers' may well appear?
Alternatively, you could contact the program makers of Long Lost Family who are really good at tracing people? You've probably already considered this and maybe kept it as a last resort?
Either way, I hope you find what you're looking for. If you need any help with DNA matches I'm willing to help if you need any guidance with it. I have over 4000 of them to trawl through but it's interesting finding out.
Good luck.
Steve
