Bob,
Don't know if your still looking for input on this, but pretty sure your unit should be mounted facing up (vertically) in the compartment. The foam cutout is removed for clearance and is where the face of the unit will be when the floor panel is replaced. The bracket should have two tabs with holes that bolt to the floor lip next to that divider frame piece between the compartment and the "trunk" where the 3rd seat goes. I believe there should be two other mounting bolts which fasten the bracket to the vertical wall down below in the well. This is how the unit was mounted in my '98 S70. Only difference was that it was on the driver's site in the well. I also believe the bracket is made to work in either a wagon or sedan. When mounted, the "Volvo" logo should face toward the middle of the car and the cartridge hole should be on the left (toward front of car). Hard to describe but hope this helps.