I am trying to mount a vacuum gage next to the drivers-side speaker and can't quite figure how the speaker grill fasteners work. I pried off the trim piece on the near side of the speaker and I found two unusual plastic goodies that look like they might be rotated, but I'm not sure what kind of tool to attack them with. I couldn't see that this was covered in the Haynes manual.

Ordinarily I would just go in, "use a bigger hammer", and chew everything up. But this board is so good I thought I would first give you guys a try.
Any help is appreciated.
Al Stensby