Block cleanliness

Hot tanking doesnt really remove rust and scale well unless it flakes of the iron as a result fo the heating. I have my blocks washed/degreased and then they are airless shot blasted. The vibrations from that, and the shot bombing thru the jackets, does clean the vast majority of rust and scale away. Then it gets washed again. But you have to machine the block after. If it was me, I wouldnt touch it at this point. But if you want to... I'd take the core plugs out and use a hanger or some sort of stiff wire to scrape loose as much of the crap as you can and then wash it out. The heavier particles will stay in the bottom of the cooling jackets if they dont fall out during the washing and assembly. There's not enough current to wash them up and out so they settle there (like the factory casting sand you sometimes find...). I would leave well enough alone because the block should be bare if you're washing it prior to final assembly. Particles can become trapped behind the bearings in the oil passages and creat havoc when the oil starts to flow.