Not sure if you're really going to be able to do that with a V8 for a couple reasons:
-The wiring for the circuit may not even exist on the V8 4Runner (see the attached parts location, connector F15)
-You may need an entire "4WD Control ECU (Rear Differential) Lock" module (see attached EWD Schematic for Rear Diff Lock Circuit)
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IF you did manage to get all the required parts, switches, and connectors, you'd still probably have to run your own wiring for certain aspects such as the Speed Signal, Communication with the ABS/VSC/TRAC module, Communication with the 4WD ECU, etc. (See attached EWD Schematic) Additionally there's no guarantee that these modules will have the programming (these are modules Toyota doesn't have a process for reprogramming that I am aware of) to properly communicate with the new module you install.
There's really three ways I can see this being done effectively and I'll list them in what I thing is the order of easiest to hardest:
1.) Install the locker and make your own wiring circuit, sans module, for engaging/disengaging the locker by mimicking the factory set-up as best as possible.
2.) Try to install a V6 Rear Diff Lock Module in the factory location and run whatever extra wires and connectors you need to make it function. (assuming the computer programming exists to communicate with it, which I am not sure honestly if it will.)
3.) Install an entire V6 4WD Module, Rear Differential Lock Module, and then wire a dummy plug to trick the system into thinking an ADD exists and is functioning when it doesn't and somehow locking out the 2WD option so as not to damage the actuator (I'm not even going to bother theorizing how how you'd do that because honestly, as OCD as I am about trying to make things look/function like it was factory installed this is a ridiculous amount of work.)
