I know I'm a little late with this post, but I also bought the blow off valve from Shark racing for my 22 K5 GT. The blow off valve for our K5 GTs with the 2.5T is actually in a really tight spot. It is towards the front way deep down next to the bottom of the inner cooler. I tried installing mine the other day and was unsuccessful. It was late at night and by the time I realized that I would need to remove the inner cooler to get to it I just decided to reinstall the stock system since I needed my car to get to work the next morning. Going to make another attempt this weekend when I'll have more time.
But I have a question for you OP. The Sharkracing blow off valve came with a choice of 2 different attachments to which I assume is just to modify the blow off sound. Which one did you end up going with? Also, did you have any issues with check engine lights after the install? I've heard rumors that disconnecting the battery during the install takes care of this issue but its only rumor. Any light you can shed would be much appreciated.