Those casting numbers are just for the part and not the assembly and are not in the parts book.
The different assembly numbers may have all used the same casting.
I do lots with these 65-72 KH disc brake systems, parts.
Tell me, what is different with a 65 spindle, than a 66-72 spindle, that you just wrote about?
I probably have had 25 or more of these brakes, throughout the decades, and never encountered anything like that.
The caliper bolts to the spindle, no matter what officially year a spindle year might be.
I never heard that.
There is NO DIFFERENCE between any DISC BRAKE spindle for ANY of the years, 1965-72.
Jim V.
hemi71x
EDIT:
Here's what a 1965-72 Kelsey Hayes disc brake spindle looks like with all the bolts attached to it.