That is definitely a procharger unit. To note, there are no procharger kits for this car, so that's entirely something home fabricated. You can pretty much make out procharger on the actual unit, and it has the strange oval shaped back of a procharger.
Photos for reference:
https://cdn11.bigcommerce.com/s-75d0...702875.jpg?c=2
http://pontiacdudeonline.tripod.com/P1SC.jpg