Hmm, tricky one on the aluminium front don't really know how you bring that stuff back easily. My block probably looks the same as yours just from running it in winter with the salt on the road.
Anyway, a good engine degreaser (or simple green) will be great at getting off the dirt, oil and grease but for the sand that hot water PW you have at work sounds the ticket...
Wrap up ANYTHING that looks delicate, CAI, some connectors, alternator etc... I don't normally cover a thing when cleaning mine but as soon as the PW comes out so do the bags to protect stuff. Keep the water moving don't keep it in the same spot for any amount of time and don't get too close either, just take your time and it'll come out great.
So just to recap, take care when PW the engine bay!