Yes, they stay on car - - unless you desire to replace the inner bushing (at front end of torsion bar) - as these large bushes must be in perfect shape and centered.
Later (OEM) 'single-piston' caliper needs the corresponding (lower) ball-joint - which needs the corresponding spindle. 'this is because of the w I d e r bolt spacing (b-joint to spindle). Then, the (corresponding) adaptor bracket attaches and of course the CALIPER is next.
I will be doing all this (and more) when converting my '70 Swinger from small-bolt to large . P.S. What is a good source for (affordable?) 4.5" circle axles for the 8.75" rear?