It is neither. The Iron Duke, also known as the Tech IV, displaced 2.5 liters and was an overhead valve engine (OHV) design with an iron block and an iron head. GM stopped Tech IV production in 1993.
1999 Grand Ams used a 2.4L version of the 2.3L Quad 4 overhead cam engine (OHC) that debuted in 1987 and ended in 2002. A single OHC version of this engine was meant to replace the Tech IV in 1992 but was retired after 1994, replaced by the double OHC version.
The 2.4L engine in the Verano is a larger version of the 2.2L Ecotec engine that debuted in many GM North America vehicles in 2002 and both are part of GM's Family II group of engines designed by Opel.