The problem with shimming is the through bolt may not clear after it is shimmed.

I didn't try on my car because I am trying to use the factory keg intake which is dangerously close to the underside of the hood.

Here are the wiring diagrams for a 73 Rallye & Standard dash. These are B body diagrams but they are nearly identical to the A & E bodies.





Daniel here is a link to the Magnum Wiring diagrams. There are 12 images so I didn't link them all. If you can't get them let me know. Wiring Diagrams