What an incredible effort by these people! I personally can’t wait until someone mods in 60fps (which is confirmed to be in the works). This really is a dream come true.
GitHub here: https://github.com/zeldaret/oot
As for where to get the PC build directly, I guess you’ll have to 🏴☠️
It’s a long grueling process of reverse-engineering. I don’t know the details, but from what I know you can see the values of things and how they work from the outside, then they figure out what each value is and then re-implement it by trying to rewrite the source code. The github says this: