My first body guy messed up the install on that piece fairly badly, so it's not easy ... but then again, there's a reason I hired a second body guy.
I think that I've read here that these trunk parts need some massaging to fit, and I believe that my second body guy had to cut it at the drop down to get it to fit. I do not know if they were using this particular piece.
Also, you may want to get a new bracket for the inner rear. They're 13 bucks with NPD (and probably comparable with MU) and, if memory serves, were hard to salvage from the old trunk piece.