I was able to get both Group 31s to fit. They are really heavy
I did not have to remove the chassis battery, but I did take out the mounting brackets to push it further to the right. I was able to put all of my mounting brackets back in their original place; so those batteries are not moving.
Both batteries were 13vdc out of the box. I am allowing the Converter's Charge Wizard to do it's thing for next 24 hours; and then I will start to test to see how much additional time I have.
My feedback from the process.
1. The positive posts were close to the back wall and fuse blocks so I had to use crescent wrench, the negative worked fine with 1/2 socket.
2. I think I prefer the post versus the screws that screws inside the battery. It was a PITA to to get the positive lugs on the screw and then try to force it into the screw holes.