When adding the PSC hydro-assist setup to the 03-06 models, you either have to modify your factory steering shaft as Blaine has mentioned, or you need to get a steering shaft from a 97-02 model.
You can see the difference below:
View attachment 216121
The 97-02 shaft is pictures on top and the 03-06 below. You can see how much shorter the 97-02 steering shaft is, but otherwise they are mostly the same.
I'm not sure how you modify your 03-06 shaft, but Blaine told me that they just use 97-02 shafts to make the job easier. For the price, I think it's a no brainer. Also, it doesn't hurt to have a new steering shaft anyways.