I bought a new '65 Chevy II radio still in the box many years ago. It had all the ground straps plus two spiral pieces that fit inside the front hub dust caps. Something about grounding the hub to the spindle. There were also some capacitors/condensers for static suppression. I think Bill is right about the ground straps as I don't recall any off the back of our engine to the firewall. I don't remember the exact details any more. It was a long time ago.
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Chevelleless after 46 years......but we did find a low mileage, six speed, silver 2005 Corvette. It will just have to do for now.