I think in 1972, they went to a slightly heavier spring...it depends on when in 1972 your car was built. I imagine you can use the 1979 springs on the 1972, but should not use the earlier 1972 spring (lighter) on the 1979.
According to the Moss Catalog, the heavier spring was put on car number 293446 and after...which I think is mid-1972.
Bruce /ubbthreads/images/graemlins/driving.gif