Factory KH 4-Piston Calipers

I did say 'functional' - (aka: rebuildable) and I do not expect or intend to simply 'bolt on' used calipers. Well - (properly) maintained brake calipers should not require major surgery as there should not be contamination and corrosion. Factory pieces can be lightly honed - up to .002". With regular fluid changes, only deterioration should be the seals themselves - primarily due to age - and not the cast-iron bores - even thru 50 years. If someone is able to offer parts, I would only suggest that the pistons be removed - to inspect and measure the bores.
Your words of concern are duly noted. :)