To start off, how many rooms are you planning to do? Not that it matters, but you have quite a job ahead of you. I would jack up the floor at the center support and see what that does to the floor. It may save you alot of time and money. As for the floor, you are going to find that you will distroy more floor than save it. The wood is 107 years old. Dry and brittle.Put some money back for new flooring. To me, a slight sagging floor is part of the homes personally. Keep us informed,Ron J.