For your amusement, here is my efforts at cleaning the rust flakes out of my 1930 L and 1938 C Case engines. Because objects tend to move downhill when "blasted", in this nose-down position the flakes tended to moved forward within the block. Most un-trapped rust could then be removed thru the inlet port and the water pump opening. Rust is magnetic so a magnet on the end of a flexible wire also helps remove rust. This effort ended 99% of any rust flakes appearing in the top of the radiators. There is line-of-sight, and enough clearance through the inlet port, to stick a small rigid tube all the way to the back of the block and blast air and or water to the back left side of the rear sleeve. A pile or rust flakes (maybe partially clumped behind the rear sleeve) is porous--somewhat like gravel. Therefore, the almost stagnant coolant within the clump, will be in contact with 99+% of the sleeve's OD area that is encountering rust flakes. Around 220-25 degrees more or less, unpressurized 50-50 antifreeze will start to boil and form steam bubbles. These steam bubbles will rapidly migrate upwards and out of the clump carrying heat away from the sleeve's surface. Liquid coolant will rapidly reoccupy the area where the steam bubble formed. The steam bubbles will rapidly condense back to liquid within moving antifreeze. Bottom line, trapped rust behind the rear sleeve is quite harmless. Both metal and oil are "comfortable" up to 250 degrees. The powerful Case water pump is a mixed blessing. On the negative, it tends to "vacuum up" rust flakes that are not trapped within the engine and put them at the top of the radiator.  
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