I located the battery enclosed in sealed box just behind the gas tank filler tube. The trunk floor is not level there, so I made a shelf so the battery sits level. The battery hold downs attach to the shelf, the shelf is bolted to the car unibody/trunk floor on each side of the rear frame rail. The trunk lid hinge arm clears the front of the box easily, and full size spare tire clears everything also.
As mentioned I ran one engine ground strap from the back of the intake manifold to the threaded bolt for the voltage regulator, and a full size battery cable from left front cylinder head to threaded bolt that used to hold battery tray. Always attach cables to threaded bolts not to sheet metal screws IMO.