I put in an oil pressure sensor a few days ago. I used the location #39 in the schematic provided. It is essentially above the starter. I worked on it from both the top and the bottom. I removed the starter from below, the cold side intercooler pipe, and elbow to the throttle body. That was the easiest way for me to access the top bolt on the starter. It's a pain in the ass to try it from below . . . at least for me. If you go this route, I'd be curious what you come up with. Once the starter is unbolted, it gives you access to the sender. Don't forget you'll need the 1/8" NPT (or whatever your gauge uses, and I'm pretty sure it is if it's Autometer) to 10mm (I believe, 99% sure) x 1.75 which is on the engine side. I used a socket to thread the adapter to the block, and a stubby wrench to tighten the sender to the adapter since you obviously can't get a socket over it, and there's no way you can fit a normal wrench in there. Again, I'd be curious what you end up doing.
Oh, and very concerning to me . . . after removing the stock oil pressure sender, no warning lights of any kind have come on. Shall we assume we don't have low oil pressure/level warnings? Because that seems to be the case on my car.
Furthermore, I while working on the car the other day, I noticed that my windshield washer fluid container appears to have a low level float sensor, with a harness plugged into it. Yet I have never had a low windshield washer fluid warning light come on. Has anyone ever had a low oil pressure, or low windshield washer fluid light come on?
I'm guessing quite a few of these sensors/senders are only installed because much of our setup is shared with other cars. And that something in the ECM needs to be reprogrammed to read/process/react those sensors/senders.
If you are going to replace the stock oil pressure sender, I can take a pic of that for you. But to be honest, it won't help, much of this will be done by feel not sight. Basically get under the car, find the starter, it's right above it bolted into the block.
And if your car is different from mine and does get a low oil pressure warning light you'll need HPTuners to disable it, which was what I was intending to do originally.