Doing an SAS would be MUCH easier (and better) than trying to install all the factory 4x4 stuff.
You can run adapters on the rear to match the front lug pattern (what I did for a while), or you can install a rear end from something else that already matches (what I have now).
If you find a new rear end with a speed sensor, you can probably adapt it. I just disabled my ABS altogether, since I don't really like it anyway.
Another option is to have your rear axles and drums/rotors redrilled to the same pattern as the new front axle. That might be the cheapest and easiest option if there's nothing wrong with your current rear end.