Hotchkis 22390 Sway Bars, Set, Blade Style, 63-72 C-10 - Manual (Page 14)

You will need to use the bushing bracket as a template to locate the rearward hole.
Place the bracket over the rivet hole and mark the frame for the second hole. Using
an 90° angle drill and a short 3/8” drill bit, drill the rearward hole. If you do
not have a short enough drill bit or angle drill, you may need to raise the rear bed
and drill from the top. (refer to your shop manual for disconnecting the bed) The
bed would only need to be raised enough to fit your drill above. (NOTE: Pictures
show the drilling down with the truck bed raised. The bushing and bracket does not
mount to the top! This is only done to mark the hole location)