Hi you don't need to guess at the birthday. NYc has a birth index available for that year. Then sign up with ny state registry (free) as the sibling. (use the sibling form)
and sign up here, (once you learn the birthday.) include it in an updated post, etc. Sign up with isrr.org and G's adoption registry. all are free. Think about doing DNa. If so start with Ancestrydna. They should have sales come labor day weekend if not before.
