Pine (maybe?) Wood Floors 1x6 - What should I do?

[Ryan King]

Below are pics of what I'm working with. It's an 1880's home and everything I've read says they used pine and the lumber store said it was either pine or fir so I'm guessing it's pine. In my opinion the floor is great in 90% of the area but the 10% that's bad is fairly bad like the last picture where I would need to replace some boards. Is this possible? Has anyone refinished old pine like this and what did you do with bad spots? I can try and use closet boards but they're fairly short.

Also pine is fairly soft even if 1880's pine was harder than modern pine. Will a drum sander just tear through these? I have a lot of paint and junk to get off the top and get to fresh wood.