Battery Box
It's supposed to be in a sheet metal box on the outside of the right frame rail under the cab , they do sell reproductions battery boxes but perhaps making one to suit the larger 12 volt battery might be wise .
When I were a poor farm laddie , we'd use an insulated milk box mounted on the passenger side running board just in front of the rear fender.... works well & looks O.K. unless it's a restoration .
Remember : 6 or 12 volts , use ONLY battery cables as big diameter as your thumb . 0 gauge , I'm not sure how many MM this is .
I have mine made from welding cables for maximum cranking power and life .