I heard a couple of cylinders fire when it sped up toward the end. Timing seems to be a good theory. The engine started dying while hot last year, so I replaced the pickup coil in the distributor. Then the engine wouldn't start after I re-installed the distributor. Although I got the engine at TDC (as far as I know), it's possible that I installed the distributor incorrectly.
Cap, plugs, and wires are all good with fewer than 10,000 miles on them. The cause of a weak spark could be due to the fact that my battery has gone practically unused for a year, with the exception of these "trickle-charge and troubleshoot" sessions every so often.
One theory is that I re-installed the distributor 180 degrees off... so tonight I decided to test that theory.