I am just not sure we have the right parts.
Fired off a note to Skinz asking them to come and take a look at this and confirm we got the correct part for what we are trying to do.
Almost looks like to me you don't use the stock rear piece at all. Maybe the snow flap just mounts directly to the new extension? Just not sure on how the strength would be though for how thin it looks.
Here are the instructions. You don’t use the old rear piece at all. The dip in the bumper lines up with the new tunnel panel laser cut dip. I’m sending you a pic of the bumper installed now.