First I’m sorry you lost your dad and you have no one to help… As a fellow Ashkenazi Jew of the Polish rite I really would like to help with the spelling of your dad’s Jewish name, but I don’t know Hebrew… Now, about the Jewish name itself, my opinion is that is must be Lipman. Why? Because Lee is close to it, and because it’s a very frequent Yiddish name. But you need a Hebrew name on your dad’s monument, and the Hebrew for Lipman is Eliezer. I asked the question about this name a few time ago because I had found many Lipmans on my family tree, and I wanted to know more about it: http://www.behindthename.com/bb/arcview.php?id=43384&board=gen
But since you’re not sure it is Eliezer (and not Levi), or something else (see link above), my advice is to ask a rabbi. If you really want everything to be according to the ancestral tradition and not “more or less ok”, you should see an Orthodox Ashkenazi rabbi and ask him about the way things should be done in the Polish rite, about the name, and so on… If you don’t know about your and your relatives’ Hebrew names you should also ask him :)
I hope it helps! Don’t hesitate to tell me if I can do anything!