[Dangerous Doug]

If you have a bad coil, when it heats up the wires will expand and cause a short. When the motor cools, the wires shrink and the coil works again---until it gets too hot.

Grab a multimeter and fire up the beast. Measure the plus and minus sides of your coil. Then, head out for a drive around your neighborhood, and drive it until the engine dies again. Check the plus and minus side of the coil. If it's not reading the same as before, you've got a bad coil and have found the culprit. Wait for it to cool, drive home and change the coil.

The same may be true of the MSD, but I don't know how to troubleshoot that.

Good luck,
Dangerous Doug