Kind of OT for this post but - Do yourself a favor and put a couple ground busses under the dash, just like a fiberglass boat or car. Old metal has a lot of resistance in the bolted joints. I usually end up with 2 under the dash (where convenient on both sides) and another in the trunk. Straight to the battery with #8 or #10 wire (depends on the vehicle loads). Then tie what’s needed back to the ground bus. Especially if you get involved in more “street rod” accessories and electronics.
Here’s the Ron Francis version from Amazon.
https://www.amazon.com/Ron-Francis-W.../dp/B00AQM9MTM