My Carly has the Red Box APC and LH systems under the black plastic panel between the bonnet and the windscreen. You need to take all the bolts out to get at it.
If memory serves the two boxes under the passenger seat are the ETS system and ABS computers.
I didn't think Saab put the APC computer in the car, it was always somewhere in the engine compartment.
I would be interested to know what Abbott did. The theoretical maximum for the DI/APC system I thought was around 250bhp?