personally, i think It's a waste of time, ie, can you rule out any illegitimate children down the line, dont forget that having an affair is not a modern pleasure, it has gone on since time began, and the further you go back the less contraception there was,
can you be absolutely certain that your grandfather was was the father of your father, I have doubts about my family at much later dates than that, ie i look more like my cousin than my brother, I won't elaborate on that, work it out for yourself,
I'm not trying to put you off but surely you can see the potential flaws in tracing a tree that far back, but if you go ahead , i wish you the best of luck.
pete.