When you get your block back from the machine shop it will be very dirty even though it was tanked at the shop. Generally most machine shops leave the honing oils on the block to keep the freshly machined bores from rusting. All of this must be cleaned off before assembly.
First place your block on an engines stand so you can rotate it around. Then get a de-burring knife (available at and any industrial supply store) and deburr every sharp-machined edge. This insures that you will not cut yourself when handling the block or complete engine later. Deburring can also eliminate potential stress risers, which can possibly form cracks. Be careful not to nick any gasket or seal surfaces while you are doing this.
After you have thoroughly de-burred the block, it is time to start washing. Get some strong detergent like Oil-Eater or Simple Green and douse the inside and outside of the block. Do not use a strong acid or alkaline cleaner like lime-a-way or liquid plumber or your block will dissolve. Be a little careful of the cylinder bores because these will rust in seconds! You can actually see the rust form with your eyes! I prefer Motul Moto Wash because it has rust inhibitors in it which retard bore rusting even though it is a powerful cleaner. Get some nylon bristle brushes and bust up the inside and outside of the block with lots of elbow grease. It is probably a good idea not to use wire brushes on your soft aluminum block but if you run into some tough crap you can carefully use a brass brush. Remove all traces of grease , grime and deposits. Brush, rinse and repeat until the block is as clean as new inside and out. Avoid the bores at this time.
Next get an engine brush kit or a gun cleaning kit and brush out all the oil galleys with. If this seems anal , it is very important and you MUST do it. Hot tanks now days are not as good a in the old days when pollution was not an issue. Modern eco-safe hot tank chemicals are crappy and blocks are not nearly as clean from the hot tank as they used to be. You will not believe the crap that comes out of these passages! Flush with water, brush and flush several times until you can see absolutely no traces of any kind of gunk, slime or crap
Finally you have to clean the bores. The bores will be contaminated with honing slurry and if you want your new rings to seat right and last, you must get rid of it all. Get a clean soft 100% cotton white cloth or a lintfree paper wipe and saturate it with carb cleaner, the petroleum based spray type, NOT THE ACID DIP TYPE! Wipe the bores in the direction of the cross-hatching and repeat until the white cloth remains white after a wipe. Immediately spray some WD-40 or other rust inhibitor type oil on the bores as even the air’s humidity will rust them in seconds. If the bores get a little brown stain don’t sweat it but be careful about letting any kind of rust form. It forms so fast that you have to keep an eye on it during the whole cleaning process. I like to use Motul Protect on the bores as this is a powerful rust inhibitor.
Now get some more detergent with lots of water and brushing. Go over everything once again. Then rotate the block around on the engine stand to drain all the water out of all the nooks and crannys and if you have it, blow the block off with some compressed air. Blow out all the oil passages with compressed air also. Immediately oil the well-dried bores with some regular motor oil.
Let the block air dry in the sun all day, periodically checking the bores to make sure they are not rusting. After the block is 100% dry, reinstall the oil galley plugs using some locktite blue to seal them. If you are not going to immediately reassemble your motor, put the block in a clean plastic garbage bag so it will stay perfectly clean. Be absolutely certain that the block is 100% dry inside and out before you do this or you will be creating a rusting chamber!