Ok, finally: I figured out it's an Andersen window by taking a good close look at that brake plate! It's embossed right on there! (Pic 1).
So, next up I have questions about improving the drafty seal on these things. They do appear to have channels already cut in the wood for either bead-seal of some kind, or a bent metal flashing/gasket. These are not great shots, but any ideas would be fantastic. See pics 2 & 3. These cut-outs are there on the top & bottom of the sashes (where they meet the top and bottom sashes) and also on the 'meeting rails'. I believe the stile seal up against the aluminum cover of the center bead - the pressure of the brakes pushes the sash up against the bead.
These have long since lost any kind of pliable gasket (vinyl/foam) material and are so gummed/caked up with multiple layers of paint that they don't seat/seal well. Since they are so easy to remove, I'll be stripping (wet scraping) them. Maybe I'll just take one down to the hardware store and see what kind of bead gasket stock they have on hand! So glad I won't be trying to use a router to cut channels!
Suggestions welcome! I am searching Andersen's site for any information on these.
EDIT: I found, on Andersen's site, a PDF with a diagram of this window - it's their Pressure-Seal window. I guess that explains a lot! It is listed as a replacement window, available in 1946, so I wonder...well, no matter!