I also couldn't machine a part for your carburetor. My understanding is that the ECU controls the fuel injector, though, and that most of the inputs and output

I also couldn't machine a part for your carburetor. My understanding is that the ECU controls the fuel injector, though, and that most of the inputs and outputs are fairly well known; and I'm told that it's a pretty simple control loop with the oxygen sensor, the TPS and mass airflow sensor. All in all, if it came down to it, I think I'd have better luck building an ECU from scratch than building a carburetor from scratch, after having fixed carburetors and fuel injected systems. Machining to those tolerances is hard. (To be clear, I wouldn't put money on me personally doing either one of those things. I fix computers for EEs, and I'm no machinist. I'm just saying, micro-controllers aren't that hard if you are trying to do a simple thing... machining to carburetor tolerances really is.) My understanding is that most cars don't have any sort of encryption between the ECU and the sensors; it's all stuff that someone with basic ee training could figure out with 20 year old equipment. If you have a popular/fancy car, people will sell you aftermarket/performance ECUs that are not recommended for use by the manufacturer, so while it's possible that it's a lot harder to do than I think it is, there's existence proof for the possibility.