Jack The Rear of the Car and Support it With Sturdy Jack Stands 

Remove the wheels and the plastic splash panels from the front of the inner fenders. 

Part of the evaporative emission system is located in the wheel well on the passenger's side.  A snap fastener holds a small filter just behind the battery cable grommet.  Relocate the small filter by tucking it behind the wiring harness after the back-up plates are tightened. 

Locate the position for the rear back-up plates by drilling the first hole down with a right angle drill from the top or center puching through the rear plate from the top and drilling the dimple from under the car. 

When the bar is re-fitted and the back-up plates line up, bolt the back-up plates in place using washers under all nuts and bolts.  The notched plate goes on the passenger's side to clear the battery cable grommet.  Make sure no wires or cables are pinched, snug all bolts then torque to 33 ft-lbs. Coat the back-up plates and bolts with a spray undercoating.  Then replace the splash panels and wheels.  The car can be taken off the jack stands now.

8.  Trim the Package Shelf

The shelf has to be cut on the sides and in two places in the middle.  Cut the sides first, then slide the shelf back as far as it would go.  This makes it easy to line up and mark for the center cuts.

Notches in the center of the package shelf are not needed to install the Ace.  

If you have a Deuce with harness tabs.  This requires a little extra notch to be cut toward the center from the notches for the rearward braces. 

Duct tape over the exposed edges.  The shelf may be close to wires,  and you don't want any sharp edges.

The stock package shelf  attaches to the sides of the seat belt towers.  The "trim straight back method" leaves a small gap on each side of the shelf, and the deck carpet is unsupported.  If you trim notches for the bars in the front and the rear supports, the edges can be bent up temporarily to clear till it's in place. After the shelf is fitted, bend the section back down and you won't have a gaps at the sides.