1972 Radiator Core Support is not exactly the same as 71.
The 72 Core support has the extra clearance needed for the 72 Grills to wrap inwards.
Below are two nice 1972 H/O cars:
The 1st car has a 1972 Core support.  The 2nd H/O has a Core Support from a 1971 model:

72 Core Support

71 Core Support