The old units were manufactured on equipment that was made from about 1910 until 1935. Some of the old equipment was used in very few locations until about 1950 even though it was technologically obsolete.
The block were for 8" or 12" (more common) walls. The units had a molded rock face. The units were 16", 18" or 24" long and 6" or 8" high. They had 2" to 3" thick face shells and 3 cores and were very, very heavy.
Some of the old equipment was saved and operated as a hobby or to supply units for historical renovations at a high price (plus freight for an 80# block).