You need to tell your aunt your plan. She may be content the way things are, what happens if you find him and he wants to meet her? You don't have a right to cause her any pain. And what about pain it could cause him or his adoptive parents?
Records may not be so forthcoming to you since you're not the parent, there are actually agencies that biological parents and adopted children can sign up with in the event the other is looking. They act as a go-between and see if the other is looking and want contact, they don't just say "Here's his address." My cousin was raped as a teen and gave her daughter up for adoption, around the age of 25 her daughter sought her out and they were reunited, with the blessing of her adoptive parents, no secrecy. But the agency contacted my cousin, respected her right to privacy, and gave contact information out only upon her saying it was OK. There are also two other close family situations where children were put up for adoption, they are open adoptions but in both cases no contact is desired with the fathers, though both sets of adoptive parents know their children have the right to search for them once they are adults.
If you continue you will need as much information as possible. Day/month/year of birth, hospital name or city and state it's located in, biological parents names, their ages, name of child on his birth certificate, your aunt may have named him and it was changed later, the adoption agency or attorney name, a doctor's name, the adoptive parents' names ... as much info as possible. What information is available publicly will be determined by the type of adoption it was, if it was sealed and he's not looking there may be little info available. 43 years ago the vast majority of adoptions were sealed and there's no records, even with a court order, many are just no longer available.
To search go on the internet, go to sites where adopted children are searching for their bio parents on their own, you might see something. Remember, you need dates, names, and locations to narrow it down, if you have enough it might be easy, otherwise futile. But talk to your aunt and get her blessing first, it's really not your call as long as she's alive.