Racks installed, time to put the batteries in. Here are the rear batteries. I used galvanized 3/4" angle iron with threaded rod for the hold downs. Still have room for the spare tire and storage.
Here is the sixth battery in the trunk. I used a 1" wide steel bar underneath the car to anchor the threaded rods. This battery just sits on the trunk bottom.

Just to be safe I cut out notches in the angle iron to avoid touching the terminal posts.
Here is the front rack with batteries. That's my son's hand in the picture.

Uh oh, when I put the batteries and hold downs in the firewall rack the passenger side forward threaded rod hits the hood.
Here is where the rod hits the hood.

Since there is a open space further out on the hood, to the left in the above picture I cut a small piece of 1" flat steel and moved the threaded rod further to the left. That worked quite well and cleared the hood. Everything seems to fit quite well.