Do you know where these guys lived before entering the service?
If they hailed from small tows,I have a suggestion...I found 3 guys from 1963 this way.
Call up the small town on YAHOO.
Then email the town clerk,or mayor.
The high schools and elementary schools.
The library etc.
In small towns people seem to know everyone who ever lived there or a relative.
Tell them the full name of who you are looking for and why.
Ask that if they know them could they forward your message to that person,and he could decide if HE wants to contact you.
Include your email address,mailing address and phone number.
Also I found one guy by typing his name at Google..thusly "John Smith"..don't forget the " marks.
It spit out a news paper article from 2000 about the guy I was searching for.
Of course his name was not John Smith(I just used that as an example)...his name was not ordinary like Smith ,Jone,White etc...it was a very long Italian name.
Good luck,don't give up.