Searched for instructions on how to do this, didn't find any so hope this helps out.

Apologize for lack of photos. Wasn't sure how things would turn out from the get go and didn't document.

pretty straight forward. I won't go step by step because there's more than one way to skin this cat.

Things to note:
Take caution on the plug connectors, not to break them. Some have hinges, others have covers, all pretty self explainatory, just takes a good minute or two of looking at it to figure things out.

Make sure the key isn't in the ignition anytime during the install to avoid seat belt failure warning light that's dealer reset only.

Although its for a gt3, there's some applicable info in the following link. some photos and instructions.

http://gallery.rennlist.com/gallery/album651?page=1

Keep handy someting to serve as padding between seats and work surface. Keep a piece of wood or pvc pipe handy to prop the seat up in the car while doing wiring. Cover the door sill to avoid scratches. (good advise, landjet)

Airbags non-functional. Lost Memory function. power recline works. slider and height adjust are manual on this seat.

Basically only 3 things to do. 1) Power/ground for passenger side. 2) Power/ground for driver side. 3) seat belt senser for driver side.

Tapped the larger red and brown wires from the main seat wire harnesson (car side). Extended wires with crimped connectors from the scotch locks, just long enough to give manuverability. These 2 connectors fit the flat pins on the plug on to the 997 seat side. It's easier if the yellow plug assembly is taken apart so the colors of wires are exposed. Connect wires red to red, brown to brown. Do this for both passenger and driver side. The extra connectors and loose wires can be zip tied neatly away. Seats are now powered.

Seperate the sub connectors from the main connector assembly on the 996 seat side. This makes it easier to remove the 996 seat buckle and wire harness. Take the 997 buckle and harness off and swap the 996 unit in. (Doing this avoids reversing the wires and having to make a custom plug.) Put the 996 buckle sub connector back into the main connector assembly. Connect this to corresponding connector on car side. Seat belt indicator sensor good to go.

Make sure to align the sliders evenly before the seat goes back in the car, 8 torx bolts back in place. And that's it.

Happy to answer questions via this post or PM, though PM may be a surer way of finding me.

Enjoy.

Here's what I used to tap for power (scotch lock):

Crimp on Wire connector used to connect to 997 seat side plug (for power to seat)

 

PM Sent, installed the seats but removed the old belt receptacle and tucked it under the seat, I'll send you my number, could use some step step directions.

 

Here I add pictures.