Cool Idea. I'm not sure you'll need schematics. You'll likely learn with that components look like and learn to test and repair them. Lots of opportunities out there. All I've seen is the wiring diagram for the instruments in the back of the repair manual.
When you get good.... I have a good MPEM from a RFI that has a faulty rev limiter. I'm sure that's an easy fix. Getting in there is a big problem for me. I also have an MPEM that works but puts out a steady fuel flow to the PTO injector. LOL
If I may suggest, figure out how to fix the speedometer pick up. We need that. I'm working on something but there again... I'm no electronic guy. Good Luck ! Share your experiences.