I can tell you that the OBX pedal covers are slip overs. There is a rubber skirt around the back of the pedal cover and it simply stretches over the steel of the clutch and brake pedal like the stock pieces. Since there is no stock cover on the gas pedal it just goes over the whole pedal.
Use lots of windex when you're doing this for lube. Also it helps if you have a warm day.
There should be installation instructions in the package. They will either use screws and bars or just slip over like grizzly says. You'll need a gorilla grip to do that one but once they are on they'll stay on.
I have the razo pedals...love them. Anyways They came with the pedals, a backing/ metal plate to the pedals (this is what connects the straps and the pedals together), and the metal straps that wrapped around the existing pedal.
1) I attached the metal straps to the metal plate 2)I had to use 3m tape that was provided in the kit to stick the metal plate to the existing pedal. 3) wrapped the strap around the exhisting pedal. 4) screwed in the new sport pedal. Took me about 30mins to do the pedals and the dead pedal. These instructions aren't exact and as detailed as the instructions given, but hopefully is helps.