my experience is that you should do your first century with a set up you are
extremely comfortable with. If the route is flat then I would stick with your normal gearing as opposed to a different one for hills. Upping the ratio could be a bad idea if there's a headwind or you find yourself forced into a pace you can't keep up. I once changed showed up to a century with new cool gloves & ended up with moster blisters.

Cool idea for a century. I wish there was one in Illinois.

jeff