What I know about my biological father

I know his name, "John."
He was in the Army and served in Vietnam.
He was older than my mother.
Their "relationship" was very short.
His parents lived two streets over from my grandparents.

I have seen a few pictures of him.
My grandmother saved a couple of snapshots and a military photo of him getting an award of some sort (outdoor area, rolled up sleeves, medal pinned on chest kind of thing.) According to her he brought the military picture over to show her and accidentally left it behind. She saved it and gave it to me a few months ago.

I cried and cried when I saw it. I had never seen anyone who looked that much like me. We have the same thick adams appleless neck. The same eyebrows and ears. Even the same texture, thickness and color of forearm hair.
But I don't know if I would actualy want to try and locate him. The thought of calling him or knocking on his door really scares me.

I don't know if:
he is still alive
he has other children
he knows/suspects that I exist
he would want anything to do with me
we have any common interests

I almost joined the Marine Corps when I was in high school. I was really into wearing military clothes. I asked for a jungle camo jacket for xmas in my freshman year. And still have it. I have worn out many pairs of military pants at work. I wonder what my mom thought when I started asking for and wearing that stuff.

I have always wondered if he knows all the stuff I ever wanted to know. As if by some cosmic force I have been interested in and learned about things that will give us common ground when we meet. If we meet.