Here’s an ex-fire Jeep for sale.  Rear axle appears to be a Dana60, which leads me to believe there used to be a large water tank in the rear - or something heavy enough to deserve the added beef.  I wonder if the rear frame is modified as well?

“1964 CJ6, 2nd owner, all original, 31000 miles (believed to be actual), dual rear wheels, 4 speed, 4 cylinder, like new mud tires, new carb, radiator, water pump, and fuel pump, fresh tune-up. This is an old Beaumont Fire Department Jeep, Spent its time inside a firehouse and never went muddin’, really nice body, very unique “dually Jeep".409-755-4700”