I have one of those, for my 70, sitting on a shelf. Masterpower. My buddy bought the same set up from another company. Drill new holes in firewall?
We did some hard searching on the computer; talked to a tech from the company that sells them to masterpower, etc. They are Chevrolet, and that stupid bracket makes it universal. I got nailed too. The guy told us to by a factory, found one at napa, and it works great.