I know someone that had a corroded fuse that would do the same thing. It would get hot from current flow, expand and break the connection. When it cooled, back to normal. Took him forever to figure it out. Check all of your fusible links, bullet connectors, relays, etc. Any electrical connection could have corrosion, or could just be loose after 35 years.
The ECU is the other main electrical component, that has two transistors similar to those in the ignition module. The transistors can go bad, or some people have reported that the solder connections can break after years of usage.
Some times you can fix these kinds of problems just by disconnecting and reconnecting everything electrical. While you're doing that you might find one or two that obviously needed help anyway.