So just speaking from what is currently going on in my life. If you want to power wash it, that’s fine.
you will find leaks, for sure. I would def research what the parts, labor, and known leak spots of the engine. What I mean by that is, I would purchase a new front cover gasket, oil pump gears, timing chain, gears/sprockets, bolts, oil pan gasket, and maybe water pump (gasket, bolts). The reason I say this is, you might as well be prepared to do the work before you power wash it. No sense of power washing it and not having the initiative to amend what you find right away.

if you find a leak in the front cover you can address the front cover and some of the components whilst it is off. It will mean downtime but it’s longer if you power wash and then don’t have the stuff.

 

I cleaned mine under the hood with Simple Green and a brush, and underneath the truck just a bunch of brake cleaner and a brush. Power steering pump gets nasty! You could try brake cleaner under the hood, but it might wreck your plastics and paint. But it does evaporate quickly.