Originally Posted by Dark Wanderer
I'll check out more deeply the coil thing.
The difference is simply that the 1.6 used an external ignitor and had a single three-wire connector to feed power and two triggers to the coils, whereas the 1.8 engines use coilpacks with integrated ignitors, and thus have no ignitor connector, and two separate coil connectors. Depending upon the year, the two coil connectors are either four pin (+12, GND, trigger, and tach out) or three pin (+12, GND, and trigger. Tach comes from the ECU)
Either way, assuming you get the engine harness along with the engine, you can splice the new connectors into your old car. +12 and trigger are both self-explanatory and present at the igniter connector. Ground runs straight to the head. If you have a '94 or early '95 engine with the four-pin coils, combine the two tach outs and feed into the tach wire at the igniter. If you get a later engine with three-pin coils, you can either diode-isolate the two trigger lines and use them to drive a transistor to create your tachout, or you can take it direct from the Megasquirt (modification required).
Oh, your CAS will move to the exhaust cam. Same connector, but you may need to lengthen the harness a few inches.
If you choose to swap the coils, FM sells a bracket to do it: http://flyinmiata.com/index.php?dept=67
You do not need the throttle body adapter from that page- you're going to keep the 1.8 TB on the engine.