Digging up an old thread, but since I'm in the middle of building a new KSP install with mods, I thought I would share my experience for people asking: "Does this mod still work?"
As of 1.12.3, YES - with some work.
On page 18 of this thread, Poodmund has a few lines of code you should change out that improve things. Its quick and easy.
As well as the other dependencies, you need to install something like Astronomer's Visual pack. This conflicts with Spectra, so you will have to uninstall that if you have it.
Here's a gallery I made of side by side pictures of what the Outer Planets look like in default, with the Overhaul Mod installed, and with Astronomer's Pack side-by-side: https://imgur.com/a/ObaVv7F
Only remaining issue is the Uranus replacement isn't tilted.