You can run Tein coilovers for the WRX on your GT, I did so for quite a while.
Bear in mind though, your range of adjustment at the front will be very small.
Here is my 97 GT on Tein Flex:
This is how much thread engagement I had on the lower brackets at that height:
That was one of the reasons I sold them to a WRX owner, the other was that the stiff springs rates (559f/448r) on the Flex will
really upset your ABS when braking on uneven surfaces, as the front wheels will tend to skip over any bumps (I believe the ABS on the BD/BG/BK series legacy is particularly touchy about this).