Ok now the more involve part. Attach the 2.5" to 3" pipe to the intake filter (obviously the 3" part is what the filter is clamped to).
Put this aside. Now take your filter out of the airbox. Take a cutoff wheel etc. and cut off the piece that the stock intake pipe was connected to originally.
Next, take the pipe with the air filter on it and put it on top of the hole that is cutout. Take a sharpie and trace around the 2.5" part to make a circle to cut or sand out. I used my dremel with the rotary sander on it.
Now draw a line around the half of the intake box that doesn't have the hole near the bottom but still keeping the bottom portion of the airbox. THis is because we want to utilize the stock mounting parts etc.
Now seperate the airbox and cut along that line with the cuttoff wheel.
Next cut out a section on the side with the hole like I did.
After I did the above i put the sections back together where they interlocked on the bottom and used the 5 minute epoxy to permanently attach the two pieces at the joint. It should look like a 90 degree angle. We are doing all this not only for making mounting eaasy but it acts just like the K&N heat shield from the heat coming off the exhaust header.