Well, I took a look through the 90 and 97 manuals and it doesn't look like an easy job. In the 90, all of the sensors are connected to the ECC head rather than the programmer. This would require relocating several wires from the head to the programmer. Keep in mind that although they are pretty close to one another when the car is complete, the wires actually travel through the dash to the main dash connector and to the programmer. This is so there is only one electrical connector to the dash for removal/installation.
Next, there is the air mix actuator. It appears from the diagrams that the actuator is built in to the programmer in the 90 where as the 97 has a separate unit. I can foresee a big problem with the mechanical connection to control the tempature.
I really didn't dig any further because of the vast differences between the two systems. This is far from the almost plug-n-play swap in a 92-94. Sensor ranges may be different too and the 90 doesn't even have provisions for a solar sensor.
Summary: Anything can be done given enough time, money and resources. Is this a mod that I would tackle? Defenately not.