Since this an International you have a service door on the rear. Take a good look inside of this area at the condition of the floor. Where the floor and the shell come together is critical for preventing rear end separation. It is often rotted by water that flows in from the bumper area.
Since this is a 73 and it is sitting low, my guess is that the axles do not have much, if any spring left. I would consider new axles in my budget.
WBCCI President 2016-2017