Never took one apart but these were "tube-in-tube" designs meaning there was an inner tube inside the outer tube. The inner tube needs something to locate in the center of the outer tube and still allow the oil to flow when the shaft moves. Most shocks have spacers that are welded to the inner tube. These are extra parts-processes. My guess is Delco engineers eliminated these part-processes by rolling the "spacer" into the outside tube (shock body) with the grooves.
Most modern shocks a single tube and gas filled.
Incidentally, Delco shocks were all made in a factory about 5 miles from where I live. Many neighbors-family worked there when I was growing up. Long gone now.
