Marilyn & Bob wrote:

Can someone explain to me why one would use PVC instead of cast iron as
the replacement piece? After all, one already has a cast iron chain
cutter to cut out the existing damaged pipe. And, while we're at it,
why is the pipe cut a whole inch shorter than the length removed?

The neoprene sleeves have a "ridge" in the center, which will
space the pipes about 1/4" apart. I would have cut the pipe
to allow about 3/8" to 1/2" total spacing.

You could use a section of cast iron; it's a matter of
convenience and what material is on hand.
Jim