John, You are gonna have a LOT of ancillary crap associated with the 12. It is managed as 2 seperate 6CYL engine managements and ignitions. To function properly you will need both ECMs, both ignition modules, the base module, the diagnostic module as well as the EIS, and EA's if it is an electronic trans (don't remember for 96) then you will also need it's module as well as the shifter quadrant. You will need to adapt an accelerator pedal switch to generate a signal as expected. If you expect to keep the check engine light off you will have to update the car to to the same evaporative emissions standards including both purge valves and the cansister shuoff valve. The ASR could be a huge problem too. Don't recall seeing a 12 without it. It has the potential to cause problems with the throttle control leaving you with a 1500 rpm ceiling,ie limp mode. You may be bending a lot of new brake lines and fabricating wheel speed sensor triggers and mountings before it's satisfied.

Of course a pair of programable managements and mechanical throttles would simplify a lot of this. How bad do you want to keep it OE? You have an enormous amount of work in front of you to go OE. You are gonna have to get your hands on all the wiring diagrams for your donor. You don't stand a chance without them.