The wife and I have reclaimed enough of the circa 1927, 3/4" thick, 2-1/4" wide Southern Yellow Pine (SYP) flooring strips from two relatively small bedrooms in our house to reuse in the new master bedroom and walk-in closet we created when we rearranged the floor plan.

The flooring in one of the old bedrooms had been finished only for a couple of feet around the edges presumably because it was intended to always have a rug in the center of the floor. So some of the floor has finish on it, and the rest has been bare wood under a rug for the past 90 years.

The entire floor in the second bedroom had been finished at one time, then sanded and refinished at a later date. I mention this here because mixing strips from the two rooms results in strips of various thickness being side-by-side due to one room being sanded once and the other never being sanded at all...and we also have "finishes" varying from bare wood to an amber color that I assume is old oil-based poly over unstained wood to an orange color that's either a light stain under old oil-based poly or perhaps just unstained wood under a shellac or varnish that aged to a darker shade of amber in the second room than in the first.

The strips from both rooms have their fair share of 90-years worth of dents, scratches, nail holes, staple holes, etc., but part of the reason we bought the house was for its old, if not historic, "character", and the remodel we've done is so extensive that the only "orginal" surfaces that we'll have left after the remodel would be that reclaimed flooring...and that, only if we actually use the reclaimed flooring and ignore the temptation to use new wood. So we're OK with the damaged boards and: a) will plane and sand just enough to make the edges of the boards match in thickness without removing as much wood as would be necessary to make the floor perfectly flat; and b) will fill the holes with wood filler as necessary, probably using a two-part epoxy filler made for floors by MinWax (unless somebody tells me that's not a good idea).

We like the natural look, so we're not planning to stain the boards, just apply finish. After hours of reading posts on this forum, I gather that StreetShoe and Bona Traffic HD are popular...but I also gather that water-based finish doesn't look good on SYP, and that I should be considering products with oil in them, either oil-modified urethane (OMU, which, I gather, is actually water-based) or oil-based polyurethane. Unfortunately, the posts I've read that recommend oil-containing finishes for SYP don't mention specific brands, so here I am asking, "What brands and specific products do the pros recommend for finishing SYP, and what are their pros and cons?" And, of course, any other advice you want to offer a DIYer about this project would be greatly appreciated.

Since you like the "old" floor look you may want to stain the floor with a light brown color that matches the old color of the varnish from long ago. I like one part walnut and eight parts neutral oil. Then you could use a water-based finish that dries quickly and doesn't smell as strong as a solvent based finish as the stain is a good sealer for water-based poly-urethanes. Any two part finish will be good.
OMU is oil modified poly-urethane which is the finish that has a yellow color as it ages. I think that the poly-urethane or natural water-based finishes have a modern look that doesn't anchor the architecture like the "older varnish" look.
You can sand the floor diagonally to get it smooth without needing to run it through a planer. The old finish with dirt and grit in the surface will dull the planer blades but using carbide would do the job if you have the equipment. Sandpaper is relatively inexpensive and easy to change when it gets dull, or gummed up from old finish. Once the floor is flat you go with the grain.You would need to sand to 100 grit to be smooth enough to stain the floor. A smooth floor will enable the finish to wear longer.