Hi James.
I can sympathise with your situation.
My father was fostered out when just a few months old and given a new name. He was very fortunate that his biological mother made contact again when he was about 12 years old, but she always refused to discuss who his father was. After she died some of her friends gave us a few "clues", and since starting research about 7 years ago we have been able to piece together an ancestry for him.
I have seen first hand how important it has been for hime to finally "know".
As well as the sympathy for your situation (which is nice, but totally meaningless i realise!) I am writing for a couple of other reasons:
1) My father would have been an Altman, or rather that was his biological father's surname. Just a coincidence. Probably. But we do know that some of that family travelled to and moved to the USA from the UK in the early 1900's.
2) Have you considered taking a DNA test? We did this to help "prove" our link to the Altman line. Not specifically to any living individual, but to a general family grouping. For us this strongly linked us with our Altman / Altmann / Joseph family, beyond any reasonable doubt. Enough facts fitted for us to be sure of that.
I can highly recommend using Family Tree DNA if you want to consider that.
http://www.familytreedna.com/y-dna-compare.aspx
This will, at the very least, place your father within certain groupings and could possibly narrow your search. You might even get lucky by matching to a family who have already been tested.
3) Have you got any information at all from birth documents? My father to this day has 2 birth certificates each with a different given name. His original given name was found to share the same middle as his biological father!
I hope this helps in some way.
Kind Regards,
Simon
Hove, UK