Mild organic acids w or w/o electrolysis can do marvels cleaning up rusted iron! When current gets added with the RIGHT electrolyte, metal may even be restored or plated. Hmmm, some nice COPPER plating that pump housing might be worth the effort, what little there is. Copper would protect the underlying iron, dissipate heat even more evenly and such. I might try this on one of my old iron housings.
My faves are the early ones, though alas! I busted an ear off the thermostat flange on the one '65/66 housing I have. Fortunately, some stuff earmarked for 440Source hit the market then, and I scored an Al housing accoutered with the same old ears, an extra bolt hole to permit its use with later model brackets, but otherwise features a form very close to the old Mopar housings. I checked the return ports when a well meaning soul mentioned that much chinesium got cast with undersized return ports to the block, but this one measured out just fine. I still want to return to iron, someday....