Jedimaster: Take a look at the bottom of the shifter where the white ball is. You will see a black pin that goes through the ball. Take a small pointed chisel or tap and tap the pin out with a hammer. It will come right out. Do the same on the stock legacy shifter and put the ball from the Legacy shifter and install it on the WRX shifter and tap the slide pin back in. After your done grease it up and reinstall it and your done. The Legacy shifter is secured with a 'C' clip which is what holds the shifter in the linkage. The 'C' clip is probably the most difficult part, and even that is easy.
Drift Monkey: Yeah I know you remembered. You are good about absorbing information. If it werent for you and the few others, then I would feel I was waisting my time even posting my findings.