I re-build aluminum Ford " Teksid" Blocks all the time. While I have seen so polished, and yes they look nice, I also believe they usually cost around $3,000.00. I like to get my blocks as clean as I can, I start with the usual de-greasers like Gunk and hot water, this softens or removes most build up. After that I break out the pressure washer and blast away, till i have everything off that's coming off. Most engines look good at this stage, but some don't. Sometimes aluminum gets stained, and looks dirty when it's not, for those times I get out the sand-blaster and using glass beads, I go over the block, either entirely of just the trouble spots, and this does a great job, it removes the built-up areas, and evens out the casting surface. Honestly, I usually blast them regardless of how clean I get them in other stages. Sand-Blasting, just does to nice a job, to limit it's use. I can remove casting scale that should have been removed at the factory, and I can even the whole surface color, so it appears to be a new block. once the block is clean, and all the machine work is completed, I use a cast aluminum paint (spray) and call it a day. If you want a really nice show engine, then you would have to even up all the outside surfaces, which would require a liberal use of surfacer/primer, and sanding between groups of coats. Some areas might even need some filler to smooth out. Lastly, I would then coat the block in a nice glossy color of choice, followed by a couple coats of clear. Good luck