Your problem is due to those plastic holders. You can easily get some bolts, nuts, and rubber washers to mount your Panaflos at any hardware store.
I have the Compucase LX-6A19, which has the same chassis with a different front bezel, and I've got two Panaflo's in my system.Without the plastic mounts, the HD cage is a tight squeeze, but it will fit. There is also no noise or vibration from the fans by using the rubber washers.