hofilbert - yes it does require some holes, I believe I used #8 or #10 sheet metal screws. The lid does not come off, it is sealed against the filler inlet like on a Charger (there is a spring and rubber seal on the cap). So, you lift the license plate, pop the fuel cap which opens, then when open it holds the license plate up as well.
Details - well I cannot say for certain what the cap came off of, but I believe perhaps a 69 Barracuda although I believe a Charger one is very similar (the flip lock sits on top of a big chrome ring), however I will not swear to this. The flip lock I used has a slight taper in the back, so when it is laying say on a table, it will lean to one side or perhaps better said, one side of the cap it closer to the table that the other side.
I made a small spacer that sits behind the cap and goes over the 4 screws that hold the filler tube into the car. I also made small extensions to the license plate bumpers to lift them off the license plate off the gas cap (1/8" if I remember). I also had to clearance the inside of the cap to go over the factory filler tube lip.
this isn't super hard, but does take a little imagination to make work. Once you have it, you will not need to use a normal gas cap (in fact you can't unless you use a flip lock that does not have the sealing part)