Trunk Mounted Battery, Location?

The right side is the time honored location. As mentioned, it's because that's the side that tries to lift.
It can depend on the spring, too. In the mid 90's, a friend and I installed Tri-City Competition leaf springs on our Road Runner. Greg Luneack, Tri-City's owner, told us to put our battery in the center, because it's weight had been compensated for in the design of the springs.
That has been a while ago, just something to consider.