Welp, turns out a bad dizzy cap was prolly the culprit. The old one had carbon tracks leading up to one terminal, so replacing that along with the rotor seemed to restore smooth running. Replaced the plug wires as well for good measure (scored a deal on fleabay for a NOS Magnecor set), and had previously replaced the coil and ballast (to no apparent improvement). However, now it's flunking emissions.