Removed one nut (circled in red in picture) from the threaded post on the interior end of the battery tray. I was then able to reposition the large battery cable to be above that smaller one, and then replaced the nut.
When turning the nut, be carefully not to let the tool touch the nearby screw head that is also noted in the pic, otherwise sparks will fly.
This did allow the battery tray to slide farther out. But, even with the tray fully extended, it was still darned difficult to check the water level in those last two cells. I see a sealed battery is in my future when this one bites the dust.