Actually I'm not going to do a DIY on the oil cooler. For one, I didn't get enough pics since my camera screen died early in that process. But also, RCZ already has plenty of pics, and the Stillen instructions do a decent job of telling you what to do. I'm just going to make some notes and addendums, some of which might only make sense when you've got the parts in front of you and you've read the instructions already:
First, here's the pics in RCZ's thread of his install. Note that he moved the power steering cooler off to the side, whereas the Stillen instructions leave it behind the oil cooler, which is what I did (because I may install other cooler kits from them on the other side later, like the 7AT one):
RCZ's oil cooler install pics
As far as oil hose routing goes, my path (after consulting with Stillen for clarification, as the instructions give only vague details from another car that don't work for us) is very similar to RCZ's. Like his, I used the 45 degree connectors at the sandwich plate and the 90 degree connectors at the cooler, facing "backwards". The only difference at the oil filter side is that I rotated the sandwich plate so that the hose connections are more towards the front of the car instead of directly below the filter, to make filter access easier. At the cooler side, with the power steering cooler relocated behind the oil cooler per the standard Stillen setup, the far line needs to go in front of the vertical bar that runs down the center of this area, rather than behind it. This keeps it from hitting the PS cooler.
Re: relocating the PS cooler (one of the first things you do once the bumper is off), be sure to buy a quart or two of replacement fluid before you start, as you will lose a ton of PS fluid while you're extending the lines. The Service Manual indicates either a Nissan-branded PS fluid, or Dexron VI ATF (auto trans fluid), which is what I used.
And in case it isn't obvious (eventually) from the parts provided and the instructions, you want to re-use the little black rubber grommets from the factory PS cooler mounts inside of the padded clamps provided by Stillen. You need to use the self-tapping screw (with a spacer) for the bottom/left mounting point, and you need to drill a hole in that vertical peice of metal and use the long M6 screw + nut from the kit for the other mountpoint. Be sure to put some wood in front of the radiator when you drill this hole, as the drill is likely to jump through and try to drill your radiator too
Also, it helps to buy a bunch of extra rubber hose (and slit it), or something of the sort, and lots of extra zipties, and use these supplies to insulate the oil cooler lines anywhere they come near a peice of metal, or even might under vibration and G-forces. Be especially sure to shield them where they come near the metal power steering lines, as the braided lines can eat through those power steering lines if they rub on them.
The final and most perplexing thing I ran into: When I first started the car after refilling the oil (you do this in stages btw, as descibed a few posts above, as the lines/cooler fill up), there was a chattering noise coming from the engine.
I initially thought this was some valvetrain chatter from lack of oil while the cooler filled up, which would go away quickly. It didn't go away quickly, even after the oil system was fully filled and pressurized and seemed to be working ok otherwise, and even after letting the engine warm up fully. I was really scared that I had done something dumb, like somehow managed to cause an oiling problem up top (who knows, like, maybe some small something fell into an oil hose while I was working, then shot up into the oil system and blocked an oil passage? Your mind thinks of all kinds of horrible scenarios at this point).
Turns out the noise wasn't coming from the engine at all. It was coming from the power steering pump. When you relocate the PS cooler and thus drain and refill most of the PS fluid, it leaves air in the system, which causes the PS pump to make awful chattering noises. There's a procedure in the Service Manual for this.
What it basically boils down to: with the engine off (but key "ON" to unlock steering wheel), turn the wheel all the way to the left and hold 3 seconds, then all the way right and hold 3 seconds, then back to the center. Top off fluid if necessary. Start engine, and redo the above procedure with the engine on. Now the chattering is gone and you're very relieved