But to answer your question, yea I can take some measurements next weekend off the 203 subframe since I need to replace my diff immediately. (Noisy carrier bearing, getting worse)

Also, on the standalone TCU ask about the diff ratio and what happens when you change it. Your current setup has no trans computer at all, just some vacuum controls and that's it. So your check engine will not be an issue because as far as your car is concerned it can be a manual shift! You will have to rewire a simple parking safety switch to let the car start in park and not in drive.