Also wanted to say thanks for your post! I just installed the Cobb shifter + Cobb bushings (front and rear) last weekend on a 2012 WRX 4-door. The instructions that came with the parts from Cobb were wrong and I don't know why they bothered including them at all...
The Cobb instructions suggest cutting both a corner of the metal plate around the shifter and also the rubber boot since, they say, this will make it easier to get into 1st and 3rd. I did cut the metal plate with a dremel, but I didn't want to cut the boot. So far, I don't find any appreciable resistance going into 1 or 3. I think that the Cobb is 'shorter' throw than the Kartboy and that's why they recommend this.
For my install, I removed the 4 screws holding the heat shield, but I didn't remove the shield itself since that would require removing the oxygen sensor and I just didn't want to mess with it... I just kept moving the heat shield from side to side while I was working underneath.
Also, I took off the old bushings and installed the new ones without removing the stabilizer bar from the car
It's cramped up there, but by moving everything around, I was able to get everything removed and then installed!
How do I like it? I adjusted the shifter to its maximum throw and minimum height and so far, it feels great
It does feel like I have to reach a bit farther to get to the stickshift, but that might just be my perception. ie, the new part seems to me like it's tilted away from myself more than the stock part.
I did drive the car with the old bushings and new shifter for a while. Even with my car with 2.5k miles on it, I could feel a big difference when I finally put in the Cobb bushings.