Umm partypooper maybe but please think a few things through before you go ahead.
What can this guy offer you?
What can you offer him? (maybe thats easy - his grandkids)
why do you feel the need to contact him? Is something missing in your life?
What if it turns out that he isn't your dad? What if your mom was elaborating or if maybe back when she thought you were his?
Having got past all that, I think a letter is a great way to proceed. Don't be offended or worried if you don't get a reply right away - it could be a really big shock o him and it may take him weeks or months to pluck up the courage to write/phone back.
If after say 10-12 wweks you have no reponse, send one more letter, saying that you would honestly like to get in touch - gives him that second chance, that "maybe she really does want to know me"
but don't hound him and force the contact.
I really hope this goes well for you and that everything turns out great.
I know the pain parents can cause, my mom and dad split when I was 18months old, both tried to get the other to have me (no it wasn't fighting over who got me - they both didin't want me!)
my nan took me and my dad in (my mom was 17, my dad 27!!!)
i didn't get to really see my mom then until I was 7 - apparently she did come over but I had been told she was a bad lady and I ran away from her??? I hardly saw her until I was about 17 and got my first horse - we spent quite a lot of time together. It all ended in tears.
Now we speak occasionally. Every so often I let her into my life, we have a few great weeks, then she lets me down again.
Last time, she wanted to be there for me and the baby, to be my birth partner, etc. Then I didn't hear from her for 10weeks. This time I am more withdrawn, I don't want anymore hurt, I am going to try and keep her at arms length, I don't think I want her close enough to hurt me again.