GM HEI no spark for 30 sec. when cold

[big gear head]

You can get a cap from MSD that has the same spark plug type terminals on it as the HEI cap. Still, seems like there should be a simple cure for this. You have already done everything that I would have done. I have a test HEI that I have installed in many different engines to either prove that the ignition is the problem or it isn't the problem. By using a different distributor you have done the same thing.