Well after getting my Downpipe from full-race I realized that it had the o2 bungs for the 18mm o2 sensor. So I searched and found a few ideas of how to make one and thought I would share a simple way to do it in case someone else needs to make one.

First the materials you'll need are:

A spark plug anti fouler (18mm) can be bought at any automotive store.
A 12mm x 1.25 tap and the corresponding drill
A dremmel or cut off wheel
A buddy to hold stuff.

First take the Anti fouler and have your buddy hold it with a wrench or something or use a vice if you have one so it won't spin as you drill it out. Use the dril bit and enlarge the hole in the center of the anti fouler. It already has a hole so it helps hold the drill bit in the center and the drill bit goes through quickly.

Once the hole is drilled take the tap and tap the end that has the 18mm threads on the exterior. Don't mess the 18mm threads up as that is what will be going into the DP.

Cut the threaded portion off like in the picture below.

You can see in the picture the original anti fouler and the new cut/drilled/tapped anti fouler.

They thread the o2 sensor into the new adapter and then thread that whole thing into the DP. Make sure and us some antiseize so it will come back out later. You can use a dremmel and slot the top so you can use a screw driver to twist the new adapter out later. If its on the o2 sensor tight enough it will come out with the sensor.

Plug the 02 sensor back in and start it up. Check for exhaust leaks, and they go for a drive and make sure everything is working right.

Hopefully this will help if anyone else needs to do this. I don't claim to be the inventor of this idea so thanks to those who gave me the idea.