4door GTT's do not use the fork on the back suspension so GTR suspension won't fit 4 doors.
as dave said, if your rear uses a fork then you can use GTR suspension. The only qualm about this is that apparently on the highest height setting using GTR suspension, the car sits a tad below stock height.
the way i see it is
SAU = focus on cars
SNSW = focus on social events.
We (SkylinesNSW.com) have had harbour cruises, fishing days, LAN nights.
Whereas SAU seems to be more focused on trackdays, driver training.