I think if you get down to the fine dimensions of the Optima, you will find that it is the same size as the smallest production battery (Group Size) made to fit your vehicle.
I went through this with my 37 Chevrolet pickup and after measuring everything on the battery rack at the local Auto Zone, the Optima case was the size of the smallest Group Size. The top hung over a bit more, but it still fit the box.
And, of course, we all know they are the best!
