If only they had paved roads in NE Tennessee,

, your engine would be nice and clean. Actually, I've seen far, far, far worse than yours.
The gen 1 LS400 engine bay really is a "work of art" -- much nicer than later models that had plastic shrouds covering all the naughty bits. I'll never forget opening the hood of my first LS in the company parking lot back in early 1990 one noon and having a crowd gather and marvel over an engine architecture that, at the time, was available only on exotic cars like Ferrari.
Probably all you need is a little spray "degunker" and brushes of various sizes to clean it up nicely ... and then a light spray from a garden hose to wash the dirt away.
It really is possible to keep an engine compartment perfectly clean -- that is, if you are not continually driving on dirt and gravel roads. All it takes is a light washing of the engine compartment every few weeks. I've done it on LS400s for nearly 20 years and never had any drivability problems from doing it. Even when I don't wash the engine compartment, I wipe down all reachable components with a damp towel every time I wash tje car's exterior.
I even wax all the paintwork in the engine compartment with cleaner wax about once a year -- probably don't spend more than ten minutes doing it.
Try a little harder!