Some late model heads had problems with cracking. If the truck overheated, this could cause warppage.
Was the water from the heads being removed? Water could have come from the head gaskets. Usually you won't have a problem with the block unless it really got hot or froze from very low temperature.
What are you reffering to when ask what is a good choice to clean the engine with? Are you reffering to the external parts of the engine or the internal? I'm assuming the internal parts. The cooling system, you can use dawn dish washing liquid make sure all the suds are flushed completely. The lube system, you should have much problems usually the water will be carried to the oil pan, water is heavier than oil so it will stay on bottom of the pan.