1981 Ramcharger 318 Runs on 4 cylinders

My 1981 Ramcharger 318 cu. In. (110K miles) is only running on four cylinders. The no. 2, 8, 3 and 5 cylinders are producing no power. Fuel supply seems good. The funny thing is, these are every other cylinder in the firing order 1-8-4-3-6-5-7-2. The distributor has a dual pickup arrangement. Could one of the pickups be bad? If I knew whether each pickup fired every other cylinder, that would help answer my question. It began by skipping and backfiring a lot, now the four cylinders produce nothing at all. The kicker is that, when I unplug the plug wires on these four dead cylinders while the truck is running, I can hear fire arcing from the plug wires, like they still have fire. A rebuilt distributor is only $60, would that be a good thing to try?