No, KH disc brakes did not have equal reservoirs from the factory. You need to realize that the brake parts listings that RockAuto and everyone else uses are incorrect. Sometime in the dark days of Chrysler, they experienced some kind of data dump, and the part number records for A-body brakes 67-72 were corrupted (possibly others, but these are the ones I am familiar with). It's why certain applications can be impossible to find, even though the parts exist -- they just aren't linked to that application. Your MC should look like the one labeled 73+ above (big toward the firewall, small in front). The A and B-body disc brake MCs did not change over the entire period, in appearance -- only the bore diameter changed, with variations per year, model, and power vs manual. The important difference between disc/drum and drum/drum MCs isn't the reservoir size, it's the presence of a residual pressure valve in the drum ports -- you do not want this in the disc port or it will cause the pads to constantly rub.