Trying to locate my husband's grandfather, any advice, free sites?

We are trying to locate my mother-in-laws dad. All we know about him is that his name is Thurman Henry Doss, not even sure if that is the correct spelling. He was in either the Air Force or the Army and for sure was in Waco, Texas in the early 1960's, my mother in law was born in 1963. He either taught or attended Baylor University during that time as well. He would be in his late 80's if he is still living, but we don't think he is alive, but would like to learn about him or find relatives of his. Any advice? Thanks