I qualify by law according to this statement on the website of the Dutch Immigration and Naturalisation Service:
Were you born before 1 January 1985?
You are a Dutch citizen by law if your father was a Dutch citizen at the time of your birth. It does not matter whether you were born in the Netherlands or abroad.
But the problem is tracking down the documentation from Holland and South Africa. I presently live in South Africa. Are there any businesses or organizations that can assist?