Unless you have some special MB test equipment, I don't know of any way to test the ignition module. GM HEIs are the same deal. Unless you have a HEI module tester, you test the pickup coil, ignition coil, and wiring. If all this is okay, by process of elimination it's the module.

The good news on HEIs is that the old four pin modules are only about 30 bucks.

Duke