We installed an OBX system two weeks ago on ShoNuff's G8, and those are Kooks rip-offs, so the install should be very similar. They are a bit different than my ARH system, but it generally worked the same.
First off, get a front 02 extension, you'll need it for the driver's side, passenger side doesn't need it.
Jack up the car and put it on jack stands, fairly high. Unbolt the four bolts that hold the metal plate under the middle of the car that spans the tunnel. It's about midway back or so.
Pop the secondary 02 sensor connectors off of the transmission, then disconnect the connector to free the 02.
Unbolt the mufflers from the mid pipes, and unbolt the midpipes from the cats. Slip the mid pipes at the rear off of the rubber hangers, then slip it off the front ones at the tranny cross member. Remove the midpipes from under the car. The 02 sensors can then be easily removed out from under the car. Some WD 40 or equivelent may be helpful.
Remove the plug wires, remove the pinch bolt and slide the steering shaft up off of the rack, being sure not to turn the road wheels or steering wheel while this is undone.
It worked best for me to unplug the primary 02 sensors from the harness, but they are tricky to get to, up behind the heads. I was able to get to the passenger side from below, and the driver's side from above with another person supporting it with a tool (screwdriver or pliers) from under the car.
Unbolt the dipstick tube from the head and rotate it out of the way. In my experience with the Kooks style headers, it doesn't have to come out. Not so with '08 GTs and ARH headers.
You can upbolt the exhaust manifolds and drop them out the bottom with the cats attached. I left the spark plugs in up until this point. Now they can come out.
Remove the primary 02s from the manifolds, apply anti-seize and mount them in the headers. Do the same for the secondary 02s.
I started with the driver's side. We almost didn't have the car high enough, but the heat shield on the firewall gave just enough that we were able to wiggle it through the tight spot and into place. It was easiest with a guy below shoving the header up and a guy above pulling and securing it with a bolt loosely.
I just realized that this is probably way more than what you asked for. Sorry.
One thing that we just had to change recently was to remove the springs that they used to bolt the ball flanges together. I don't get that system. They were tightened so much that the springs were completely compressed, and the exhaust was still able to shift and then rattle. We pulled out the springs and tightened the clamps without them. The tail pipes stayed in place and stopped banging against the Camaro diff.
We also never got the cinch clamps to fully close, even after visiting a muffler shop and having them snug them down. Hopefully Kooks has this part more accurate than the OBX copies.
We reused the stock manifold gaskets too, and they sealed up great.
Hopefully any of this dribble was helpfull.
Have fun.
