OK some updates to this....
First of all it is nice this tutorial has been used. When I wrote this there was only one video on youtube describing how to make a Scuf style controller. That video was only about adding HUGE buttons to the bottom, not adding trigger stops or paddles. Now there are many of them and a few you can tell they followed this tutorial. Also I've seen this tutorial posted on a few other sites as well. It's nice DIY people are able to mod something that they may not be able to afford otherwise.
All screws are 4-40 by 1/4 long.
I now move the switches up higher. They are basically slightly above the screw in the battery compartment for reference. This allows the chat pad adapter to fit. This also lets the left switch fit in the corner of the D pad support so you don't have to file it down. I've seen people cutting the support off and I don't know why you would do something to make the D pad worse than it already is.
I also sand the bottom switches down to where they are just outside the surface of the controller. This requires less flex of the paddles which would crack over time and keeps the paddles closer to the body so you don't accidentally hit them when setting the controller down.
As stated previously, I have added nuts to the inside. At the top most screw for each paddle. My personal controller stripped out and I did this as a makeshift fix and started adding it to others I've done. Originally I used spring nuts (the one on the right) but found they would stay opened up after a few times defeating the purpose. So I started using a standard nut. This causes issues with the CG2 controller. The CG2 has part of it's RF components in this location. I ended up moving mine out of the way. Once I attach the paddles I cover the nuts in hotglue
I also added a second screw below the first. This keeps the paddles from rotating when tightening them down.
Under the paddle screw heads you can see plastic washers, this allows me to loosen the screws and pivot the paddles slightly left or right based on user preference.
Also since some may ask, the white paddles in this pic are actually cut from an old xbox case I had given to me. I wanted to mix it up a bit since this controller has a black and white theme to it. Also the bottom of the controller is covered with duplicolor Truck bed liner. My hands sweat when I play and all paints I tried would rub off. I used a rubber coating and it would dent easily. The truck coating has held up for now. if you are spraying it on a white controller I recommend using black vinyl paint over it first.