it sounds like the problem is a lack of battery tray to attach the rear J hook through. I'd look farther down into the engine compartment for a suitable location and create a longer J hook if you can-- all thread is sufficient.
If worse comes to worst, a replacement tray should solve the problem without any new holes being drilled into the "frame" rail.
Once you've got a method to secure the battery, cover the J hook that's close to the side terminal on the Optima with fuel hose and it will be insulated against shorting to ground.