I just installed my Perrin crank pulley last weekend. The biggest difference is that I have a 5EAT. With the AT trans there is no way to stop the flywheel except for one, that I found. I took off the intercooler; which was easy. There is a rubber plug almost directly straight down from the intercooler. There I ended up using two screw drivers place in the flywheel to stop the mass movement. The biggest problem in taking off the stock crank pulley is the mass muscle to loosen it up. It took all of me and my ass to loosen the stock crank pulley bolt, while a buddy was holding the screwdrivers in place. Once it was loose the rest of the job is "cake".
Reinstalling the belts was done by eye and feel. Luckily I had a buddy (dv8ingvector with me) that has a LGT. So I went and checked his stock belt tension by hand and tighten my own belt. Checked and double checked, then I was good to go.
As far as I am on modding I can not tell you if the pulley alone did anything, but I have seen dyno prof that it does something. That is why I chose to do mine.
PhilT and myself, MT and AT will show you enough for the non mechanical mind to accomplish this simple but effect mod.
If anyone needs help, PM me and I will help you through this. "Cake"