Jean-Yves,
Welcome to the forum. Some pictures of you "K" car will help, along with a partial VIN (use xx for the last two numbers). In the meantime, remove the rear seat back and check the two additional sections of sheet metal (called doublers) where the muffler brackets are located as well as the two brackets. Another check is the rear hanger for the exhaust. Depending on the date, you should have brackets at the rear of the car near the rear mount of the springs that look like the ones in the picture.
Again, welcome,
Jim