Wow!! Would love to park that baby right next to 87-4431. Along with Stanley, Nathan is one of my all time favorite bassists. I picked up the 5-string after trying to play some of his FourPlay lines.
But if I were looking to spend 20K, it would have to be a brand new 5-string Series II Balance K with Heart Omega and a whole lot more.
Couldn't help but notice that this one has a non adjustable nut, which would usually mean very early build, but it has a plate at the end of the fingerboard, which would usually mean late 80's at the earliest. Wonder what the build year is.