thanks for the detailed advice, Rhm!
The crank was absolutely coated in grime to the point where it was black/brown in color. I cleaned it with Simple Green and Goo Gone, and then wet sanded it with 1500 grit sandpaper, followed by a bronze wire brush, and then finally Simichrome polish. Now it has a mirror finish!
Next question - once I get my hands on a matching granny ring, any suggestions on a hack to mount it without spending the $50 on a TA triple chainring bolt set up? I mean, is it even possible, or is the hardware so proprietary as to preclude that?