The diesel engined cars are not as tough on the rear ends because they don't make as much power as the same car with a gas engine. I have never had any rear end problems with any 123 diesel car that I can remember, and I've own/owned six of them.
Uh-oh, I didn't notice that this was a '75. I owned two of those, both gas, never any rear end problems with them either. I expect that the same theory applies, same rear end, but the diesel delivers less torque to the rear end.