I have some more questions:
Would simply unplugging the ECT ECU solve the electrical side of this swap?
Making the starter circuit seems easy enough, but I'm not so sure how the car's computers are going to handle this. Is the engine ECU only listening for signals from the ECT ECU, or do they interact? I'm also seeing lines from the ECT ECU going to the throttle position sensor, check connector, stop light switch, and the speed sensor in the dash cluster.
Would swapping in the engine ECU from my 5-spd parts car help? They are both 1987 models.
The Haynes manual doesn't cover this part.