it depends which 911. if the headlights are the same the bumper will work. Many people have the GT3 bumper from the 1st version GT3 911. The 2nd version and third version(997) won't work. You can also add a SuperCup lower lip spoiler.
I'm working on a project to include louvers from a GT2 911. The mounting points for the retaining strip are the same but since the headlights on the Boxster and the GT2 are different there will need to be some cutting to make room for the headlights.
GT3 bumper and SuperCup Lip spoiler
GT2 Louvers