I've been digging through the suspension parts diagrams for the 2nd gen cars and thought I'd post some notes. Some things are the same, some things are different, some things need more research.
I will do my best to keep this updated and hopefully will have some of these parts in hand soon.
Interesting things so far:
1. New rear top mounts. They MIGHT transfer over just fine but 2nd gen rear top mount part number is not listed as fitting 1st gen. Front top mount is also a new number but is listed as fitting 1st gen. Front upper spring perch is same 1st vs 2nd gen as are the upper spring pad things (front and rear).
2. There are 2 different rear springs listed and I'm not sure why. Both are listed for manual and auto. Not clear if right vs left.
3. New rear lower control arm is a new part number and is NOT listed as fitting 1st gen. The numbers match 2015 to 2020 chassis WRX and STI. They likely will still fit, and aftermarket adjustable arms are generally the same part for WRX/STI and BRZ.
4. Different front control arms, possibly due to new aluminum uprights? Listed as not fitting 1st gen.
Obviously that's not EVERYTHING. Will add more later.
And sorry Toyota folks, I'm just more familiar with the Subaru parts resources. Most parts should cross over from BRZ to GR86 but we do know the springs and swaybars are different.
Please do note that these part numbers may (and often do) change and you should double check before ordering anything online or from your dealership.
- Andrew