The Trans Am switches from a 1979-81 model to a base model 1973 Firebird when it enters the construction area and in a public park staircase (note the rear quarter panel, absence of a front fender vent, and the rear bumper (after the vehicle is crashed).
When Beau finds out that JJ plans to race Beau's Porsche in Mr. Feld's new Trans Am, Beau gets concerned and asks Anne-Marie to cause an accident that will damage the Trans Am. This makes no sense, since the Trans Am is a late 70s model and would not stand a chance against any Porsche from the 80s, since all model Porsches from that time could go from 0 to 60 mph in approximately 5 seconds and have twice the horsepower, as opposed to the late 70s model Trans Am, which would take over 8 seconds to do the same. Anyone who owned a Porsche would know this.
When the trans-am is bouncing down the stairs in the park, you can clearly see someone fully in the drivers seat, and possibly someone sitting upright in the passenger seat as well.
Archie is in the back seat, reaching over to drive (it's clearly not him) and Chucky is shown fully prone on top of Anne-Marie in the passenger seat...