I had ordered a P3 which arrived today, along with the Toyota wiring adapter. Surprisingly, though, it also had a separate ground wire from the P3 connector that I will have to locate something to which to ground. I see a couple of bolts which hopefully are on enough metal to work. Oddly my previous controller didn't have that.
I expected to mount the P3 exactly in the same spot you show, but I have an airbag under the steering wheel that it would partially block. Therefore I am going to have to slide it to the right quite a bit, and thus also up quite a bit to avoid blocking the reset switch for the tire pressure system. That should work I guess, if there's nothing behind it when I drill the holes. Or, I could put it on the left, but I like the right better.
The P3 came with two different mounting brackets. Interesting. I suppose the newer style is to facilitate changing it between tow vehicles. Since I have only one tow vehicle I don't know that there's an advantage to either type.