Is it out of the truck? If its in the truck, clean it best you can with scrapers and the shop vac, then like Alvin said, wash it all down with Kerosene or like product. If its on a stand, you can get at it a lot better with a stronger cleaners.
If it was mine, I would soak it down with degreaser and then hit the car wash. After it was clean hit it with spray oil to stop any rust. I have washed a lot of engines this way and never hurt a one of them. Just get oil back in it and rotate it around to coat everything. I have said it before, engines are very tough and can take a lot of crap before they die, a little soap and water isn't going to kill one.
Joe
