I wanted to stick some 7th gen GTS seats in my AT as, like most, my stock seats were thrashed. The GTS seats fit the bill as they're cheap ($400 or so for a like-new pair), very light compared to the stockers due to the design and lack of power stuff, and they have a much thinner construction, which means more headroom for tall guys like myself.
I did a bit of research into stuffing them in, and didn't really find anything meaningful, save a few suggestions that three of the mounts bolt right up. This is not the case, so, here's the process for stuffing them into an AT:
The first step is preparing the GTS seats. The rear brackets will not work at all without heavy modification to the car, and the AT rails won't work at all with the GTS seats. As such, the best solution I found was to use the GTS seat rails and fabricate new rear brackets. Getting the old ones off is something of a PITA. The best method I found was to drill out the rivets, then drill out the spot welds on the rails, and finally pound a blade punch (or screwdriver) between the rail and bracket with a 3 pound hammer.
You'll also need to swap the seat belt buckles from the AT seats to the GTS seats, as the GTS buckles are too short for the AT tabs. It's a simple matter, though the AT buckle brackets are slightly thinner than the GTS brackets, so you may want to source a washer to take up the slack.
Once the seats are prepped, you can fit them up. There's only one bracket hole which is a near to perfect fit, the front tunnel side. The placement pin can be popped in, and you can then bend the tab down slightly with a BFH, at which point the stock bolt should go in easily. The door side mounts are a bit more difficult, as the GTS rails are about a 1/2" narrower than the AT rails. However, if you give them some TLC with a BFH, the tab can be aligned properly and the bolt can be torqued down, which will bend the tab as it needs to be.
From there, new rear brackets must be fabbed. It's next to impossible, at least without significantly raising the seat hight, to use the stock rear bolt locations. So, you'll have to pop a few holes for them through the floor. I fabbed my brackets out of some 1/4" x 1" steel barstock. The door side is a simple S bracket with two 90 degree bends, and the tunnel side two 45's. They're fairly easy to make with simple hand tools, but you'll need an oxy/map or oxy/acetylene torch to heat the steel enough to bend it properly. After they're bent, just mark and drill them, and give them a good coat of your favorite rust paint. I used POR-15.
Mounting the brackets to the rails is something of a PITA, as you need to have enough room in the rail channel for the rail to slide over, else the seats will not slide completely back. With a little creativity, you can slip a M7 bolt into the rail, but the proper way to do it would be using a steel hot rivet as is used on the stock brackets. Either way, in a collision, the rails aren't subjected to much lateral sheering force, so they're probably just as strong if not stronger than the factory brackets using bolts.
To secure the brackets to the floor, I used M10x1.25 bolts of the same grade as the stock ones, though I inverted them and put a bigass washer under them. Then, I secured them to the floor with another washer and nut. This prevents the bolts from getting bent or rusty and makes removing the seats in future quite easy.
So, 7th gen GTS seats in an AT. I figure I gained about 2" of head room, which was more than worth losing a bit of lumbar support of the stock seats, to say nothing of having something to sit on that doesn't look like it's been run through a blender.