The main thing is the floor mounts. The width is very close on the holes. For the rear mounts just a bit of die grinder work to open them up towards the centre of the car is good. I used some beefy washers as the opening is already pretty big. For the front I ground off the original mounts (2 large rivets per side) as they were way off and flat, then we welded on some 1/8" thick about 30mm wide and 100mm long flat bar with a bend to match the front mount and a hole in the right spot. A lick of paint and it was good to bolt in. Now, the seats in the full rearward position (or at least as far as they can go) are wide and interfere with the carpet a bit. I also cutoff the lever and mechanism that you would use in the BRZ to flip the seat forward from the backseat, since a) they are not needed and b) they interfere too much. The plastic side cover panels have to be pretty severely modified as well, I was too aggressive on the drivers side so I have ordered a new one. Also a bit too aggressive on the passenger side, but in a different way. I had to remove the rear side panels on the console as they were in the way. A shorter person may be able to get away with less severe methods. Also I used the Porsche seatbelt parts, the mount hole had to be opened up slightly. Getting the harness out was problematic, I ended up cutting the wires for the adjuster motors as I could not for the life of me figure out how to depin them. If I ever go back to stock I'll just rebuild them.
I forgot to take pics of the assembly before putting them in, if I have to take one out I'll do that.
Some pics:
Drivers side cover:
Drivers side front mounts:
Drivers side rear cover:
Drivers side inner:
Passenger side cover:
Passenger side front mount:
