Yeah man mount that s*** under the hood. Its under the hood in every vehicle that it came in. I mounted mine using the ac delco plastic mount, cut off the tabs off the side and used counter sunk holes and used existing firewall holes so didnt even have to run any new rivnuts. That was pretty easy. I ran the Fuse box under over by the PS Box too. Mounting it here keeps it out of the way and keeps the engine bay clean. Its tucked behind the fender well so will be clear of any dust or water too.
I havent gotten around to cleaning up the wires yet because im kind of being lazy right now, and its not hurting anything. Probably going to make a plate to cover this entrie corner so all of this stuff is hidden and ill have a flat place to mount something in the future.
You will need to get a small brake line bender in that area and put 2 90* ish bends into the brake lines right here to get them out of the way and give you some more room. Unfortunately these brake lines are long as hell, so you cant just remake them unless you do this before the new motor is in. Wish i would have done this instead. This woulda been the move. This is also a great opportunity to ditch the garbage toyota brake level sensor wiring plug and put a Delphi GT150 plug in its place. You can see it tucked in on one of the pics.
If you look at the bottom right of my PCM youll need to clearance one of the cooling fins with a flap disc to match the curve of the fender to get it wayy down there and out of sight.
Another benefit of doing the PCM here is you can snake the wiring harness through the OEM Heat shield right there and have it protected from exhaust heat, just make sure you use a good abrasion resistant loom
The Tac module is conveniently mounted in the holes for the old hood springs and right next to it. You can run wires through the fenders right there in the hole for the old carb fan and hide them pretty well.
Fuse box mounted and the PCM back there in the corner. Once i make the plate to cover all of that, it will all be hidden under a flat plate. I wanted to mount the PCM inside the truck at first too, but it was going to be way too much work depinning the blue and green conectors to get it through the firewall and not worth it to me. My plan was originally to mount it under the dash under the speaker cavity that doesnt have a speaker in it and come through the firewall on the passenger side.
This was all done with the Painless Harness. Theres about 1.5 feet of extra room on the main thick part of the harness that i have under there but other than that, the big area where the legs all split off the harness is directly behind the motor in that big cavity and everything splits off right above the bellhousing, its really nice becasue you can run the Injectors, coil wires, ECT, Alt, MAF, TB, and all the engine wiring through the intake cavities behind the injectors and s*** to really hide them nice. Flip your injectors to face the back of the truck and your wiring is like 90% hidden.