Cool Car, I own a 72 small block one myself. There are a few items that changed mid to late 72. Check your fenders on top with hood open where the ruber stops are located and the underside of hood. The first 2 digits will be the month and the 3rd will be the ex. 1 for 71 etc. I recently had to do this for a powerstering hose. I imagine you don't have a plate on your radiator niether. The dates should be relatively close together if parts haven't been changed. A local mustang shop might help as well.