Flip Top Gas Cap Conversion

So, I purchased the flip top gas cap adapter from this website and I'm a bit confused...

http://fliptopcapadapter.com/faq.html

It says it can utilize either the 3 or 4 bolt whole pattern (I have the 3) but it's just a solid piece of delrin. Am I suppose to drill holes into this to mount the gas top onto the car? So that would be the four bolt holes perfectly aligned to mount it to the car and the three bolt holes to mount it to the adapter?

Any ideas from someone who's done this swap. The only instructions were the picture shown in the link.