Just to close the loop... a set of 2002 STi front and rear seats has been fitted in the GC8.

Here's what I learnt:

Front seats

• The 2002 STi front seats are narrower than the ones in the GC8 but they bolt straight onto the existing holes. You can use existing GC8 seat bolts.
• Get the plastic covers for the rear bolts of the front seats off the STi as the GC8 ones do not fit the STi seat rails. You need these for professional finish.
• The front seats are higher on the backrest, more snug on the legs. I find them to be a better fit for my frame.
• Reuse the GC8 seat belt latches that are bolted on the sides of the front seats as the the STi latches would not fit the GC8 seat belt buckles.

Rear seats:

• Remove the GC8 rear seats held by 4 bolts and 4 screws holding the boot carpet to the seats. The striker plate for the GC8 split fold rear seats needs to come off too.
• The GDB STi rear seat backrest will need to be covered on the back part as the foam will be exposed when you open the boot. Plus it sits higher on the rear parcel shelf with the foam being seen from the back window. Not a pretty sight. I used a blue thin carpet material from Spotlight at $8 a meter to cover the foam.
• There are existing bolt holes on the GC8 you can use to bolt up the STi seats.
• The spot where the backrest hooks on to the panel is the same. Make sure that the hangers on the rear backrest are hooked on properly to the frame.
• The top of the backrest is tight against the C pillar but fits okay.
• There is a part near the rear door sills that needs to be covered with carpet as the STi rear seat shape exposes some wires normally covered by the GC8 rear seat.

Overall it is a good upgrade in relation to some weight savings and updating of the interior. The hardest part is covering the foam part of the rear seat backrest.

Cheers
Jonathan