KR512 internal circuitry
I have now measured some of these devices and created a crude datasheet. I am still searching for a suitable place to lodge this, and I will update this answer when available.

In summary, the device has a peculiar divider system, with a fixed divisor followed by a selectable additional divisor. The oscillator section is also strange. It is clearly designed for a particular application, and cannot be considered as a universal component - unlike the MK5009.

EDIT: The PDF is available at https://github.com/henros32/KR512