I went to the hardware store where they have those million drawers of things you have no idea where they go of what they do. But this time I knew what I wanted to find. In the box with the stainless screws that hold on a license plate there are the plastic or are they nylon parts that the screw goes into.
You drill a hole, 5/16 I think and push the nylon insert into the round hole. It is bigger so it grabs the edges of the metal. Working the pointed screw into the hole and turn it slowly. That cause the nylon to bite even more and once your threads get cut into that piece you can really crank on it to make it hold. I found the three big holes did ok with the license plate screws and for all the others I went with another size down that only needed a 3/8 inch hole or less. Be sure to paint any holes you make, don't want rust coming in on you.
Getting the Air Dam up and marked was a bearcat. I think I moved cardboard boxes and boards around for the better part of an hour until I go it set just right and was able to mark the flange holes with a black marker. I did need a lot of work with the 1/4 inch ratchet and a Phillips screwdriver point to get them to go in.
My big sis thinks I am nuts for driving this thing. But then she never did think as logical as I do.
Does this help?
If I had to do it again I would look for hex head screws and pre-thread them then put the air dam up to them in place.
I do get a few comments on the car. Ranges from WT hell is that bra on there for to, that is sweet. I works for me so far. I dropped a set of gray GTI seats in it a couple of weeks ago. I have a third that I sit on here in the apartment.
Still haven't had time to do the carpet or the wing window as it was pouring all weekend here.
Edit:
Didn't answer all the questions. The bumpers came with the Zender kit I picked up off Craigslist. Those were not quite direct replacement. They might have been if I didn't do the kit but the bumpers rubbed some on the fiberglass so I had to enlarge a couple holes to get them to install farther out from the body. Nothing that a grinder or dremel couldn't do easily but with a file a real pain.
Here is a better Idea of what the kit looked like, the car too, before paint. BP. I used small self tapping screws to get the kit on initially but then did a fiberglass and body filler to secure it and blend the line from metal fender to fiber flares.
And yes the neighborhood hated to see this thing parked on the street this way. They gave me the most thumbs up when I brought it home in it's present two tone look.

