Re: repairing/replacing original strip flooring
Many older homes don't have sub-floors. Yes, you can replace planks the same way, you just need to cut the planks from center of floor joist to center of floor joist so both ends are supported and can be nailed down.
It is best to use planks from some unseen area like a closet. They will be the same species, size, and the same age. Other wise you will need to know what species of wood you have and the width and thickness of the plank to buy new replacements.
You don't mention why you need to replace some of the planks. Some repairs can be done without replacement.
Be sure you live your life, because you are a long time dead.-Scottish Proverb