I do not know how to disassemble that lens, it is back-focusing which means the optics need to be moved out farther from the image place. If it cannot be adjusted with a simple shim, then using the spacer between the lens and adapter will work. Try that first, if the RF and Focus do not agree : then put the same amount of shim material on the RF cam.
A real "hack". Try to find instructions for moving the optics from the focus mount.