If you just leave the hard drive out by the sea, it should happen by itself. 80% should only take a few months.

Perhaps you are underestimating the level of expertise required to write an operating system for modern hardware.

The core challenge with Linux is that it is a massive code base. It supports multiple CPU families and within each of them dozens of architectural variations and then there are the thousands of device drivers.

It might be more realistic to go back to fundamentals, build a secure kernel, e.g. based on seL4 and then build only for modern hardware. Let Linux handle the accreted bulk of being over 30 years old.