The differential casting and the subframe are a
system to locate the lower control arm pivots. The lower pivot pin passes through the differential bracket and the holes in the subframe. Because the width of the differential casting may not exactly be consistent, shims are used between the casting and the bottom brackets (and at the top of the casting too) so that there is no residual stress between the bracket and the subframe. The bottom line is that the lower control arm is located by the subframe, with the assistance of the differential casting.
Because of the difficulty of measuring the length of the trailing arms on the early cars, the only thing we specify is the thread showing on the rear rod end and the threads showing past the front lock nut.
If you don't have an older manual, I'll have to dig up the specs, since we haven't used the ball/socket system in quite a few years and I will have to go into some very old backups.
