Use the power antenna mount as your ground, rock solid bolt right there.

and yes Audio Art was a good brand, the 240 was part of their standard line, the 100HC and 50HC made them a very popular company back in the day. They were well designed amps, not sure what happened to them. But the head engineer did move onto other projects.....

Previous Owner of 00 SVT Contour #1077/2150 95 Contour SE '01 3L