I have most of the battery rack built now. I will have 9 of my Optima D31T on the bottom row as low as I can, then 3 on the top of those towards the firewall. I’ll try to post pictures as soon as possible once I take them. I am using all of the factory motor mounts to mount the battery rack to give extra shock absorption for the batteries. If the old motor mounts seem to squashy, I’ll buy some 2 part polyurethane to replace the rubber in the mounts. I put 9 of the batteries into the engine bay to see how it looked and it pulled the front of the car down close to factory height, but it was still just slightly high. Hopefully the front won’t sit too low with the extra 3 batteries on top of the rack to make 12, and the motor/transmission in the center of the car. I planned out the battery layout so the wires can be as short as possible and there will only be 2 of the jumper cables that will need to be run over the battery hold down.
The rack fits in there tight with about an inch around everywhere, I also had to modify my plans slightly so the front corners of the rack would not hit the headlight motors. All in all I am happy with it.