The interference they are talking about is to the radio. It will not interfere with the ignition.
If a long wire is connected loosely to the engine, it will make and break contact under vibration. Static electricity will build up on the rod and cause sparks when the contact breaks.That spark contains much rf energy and will interfere with your 72 system.
You can stop it by insulating the rod with a plastic connector or bond the rod to the engine with a flexible wire