66 to 71 swap

redfish-- what are you talking about ---- the lower ball joint for drum brake cars is the same from 1962-1972 whether 9" or 10"-- so swapping ball joints has no effect-- the difference is the 9" spindle V 10 " spindle assemblies are different, all else is the same.
In fact you can use a lower disc brake ball joint as they use the same lower control arm also.
The rubber line is differet between the 2 also.

upper/lower ball joints/ upper lower control arms are the same between a 1966 10" brake system & a 1971 9" brake system
62-72 lower ball joint w/o disc--- K-785 rt k- 787 lf
w disc K-7021 rt K- 7023 lf
moog #'s