I drilled one hole on each existing plastic liner to connect a fastener. On the back of the liner you can see exactly where the hole needs to be drilled. Don't drill the hole to big or else the fastener will not connect. The rest plugs right in. I guess you can order those liners off the track model if you don't want to drill.

Driver side
2 - 10mm nuts
2 - plastic fasteners
1 - rear driver side diffuser 748A0 CD810

Passenger side
2 - 10mm bolts
2 - plastic fasteners
1 - rear passenger side diffuser 748A0 CD800

You will need to be going 100+ to feel any difference. Haven't tried yet.

 

This is very nice, I have been thinking of the same, thanks for the part numbers. How much were both diffusers?