I know they used to put heat shields on the batteries on Mopar Police & Taxi package vehicles. Maybe you have one of those? Could be at one time, an item that the mechanic servicing the car, just left off when it had to be removed for whatever reason. I don't ever remember seeing that kind of heat shield on a slant 6 either. If you have it, keep it in place. It might be to shield the battery from the exhaust manifold heat.