Since I last posted about the floor, I have done quite a bit of research and work. At that point I was debating what I should do with the cracks that had oppened up between my floorboards. I was hoping to fill them with a dark epoxy that would stay flexible and move with the seasonal changes in the wood. I nixed that idea because of the cost. Other fillers would not stay flexible long enough in the wood. Eventually, I found a company in England that sells long wedge shaped pieces of yellow pine that you cover in glue, pound into place and sand down. I didn't feel like having some little pieces of wood shipped all the way from England, so I grabbed some old boards and sliced them up on the bandsaw.
Since the cracks were not necessarily consistent over the length of each board, there was a lot of custom fitting to do. It took a couple of sessions in the summer heat to get it done, but now the upper section of floor is wedged, glued, and planed.
I think it looks great and it feels nice under foot!