Can you try the steps I outlined and confirm that it works for you? Perhaps something's messed up about the version you're on. Once you have a working version we can go in and poke at the differences to see where the problem might be.
I can't share a copy of the repo, but I'm going about introducing FFI the opposite way: pick Arc 3.1 and add any files that are needed to get just FFI and mysql-ffi.
That's a good approach. Keep at it, I'm sure you'll figure it out.
One way to get help with it: describe simple step-by-step changes to the repo that cause errors. Download arc 3.1, add this file from here, type this in at the repl, etc. Don't forget the actual text of the error you see as well.
