share your experience, any improvements?
also did you have to change strut tops as well or stock ones fit?

I don't think it would fit.

it will

Did you ever try this? Did it work well? What mods were necessary?

We put 02 WRX sedan struts in a 99 OBS. They fit fine and are a terrific improvement over stock :p
The only modifcation they needed were spacers on the rears between the top of the strut tops and the top hat. I'm not sure if its the same for the RS or not. They also needed the brake lines zip tied to the cut-out bracket.

Did you use the WRX or OBS tophats? I got some STi GC strut tops for my '01 RS secondhand a while back, but they had been converted for WRX use. The bolt patterns were different.