Hello, you've asked for the source code of the original mod. By a happy coincidence, I didn't delete the repository when I finished translating the mod, so you can find it here:
https://github.com/Felix14-v2/AccurateBlockPlacement

UPD: found another fork with more recend changes:
https://github.com/BurrConnie/AccurateBlockPlacement

Thanks for taking the time to comment here!
The BurrConnie fork is completely up to date and is exactly what I needed.