Here is my take on this. I have purchased drums from Randy and I am very satisfied. In response to grey cast iron or ductile cast iron here is my findings:
Cast Iron drums: The Model A Times has several articles on this subject. Wikipedia also helps with the terminology.
1. The Model A Times Volume 3 Issue 4, Fall 2007, Page 22. This article compared the three available sources of drums and presented data to allow you to select the drum that suits you. It should be noted that the article states that “These, Mel Gross drums appear to be as good if not better than any aftermarket drums for modern cars purchased at AutoZone, Kragens Auto Parts, Napa Auto parts or any of the many other Auto parts suppliers. Most are made by the same manufacturer in China.”
2. The Model A Times Volume 4 Issue 1, Winter 2008, page 20. This article “What is Ductile iron?” presents information of the difference between ductile iron and cast iron. In simple definition, the properties of cast iron are low melting point, good fluidity for excellent castability, excellent machinability, wear resistance, while the structure precipitate cracks, leading to cast iron's characteristic brittleness. Ductile iron inhibits the creation of cracks and provides the enhanced ductility that gives the alloy its name. Ductile iron is tougher, stronger, and lighter weight than cast iron. The properties of ductile iron make it an excellent choice for casting of crankshafts and brake drums.
3. From the web site:
https://en.wikipedia.org/wiki/Cast_iron
Cast iron is a group of iron-carbon alloys with a carbon content greater than 2%. [1] Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its colour when fractured: white cast iron has carbide impurities which allow cracks to pass straight through; grey cast iron has graphite flakes which deflect a passing crack and initiate countless new cracks as the material breaks; ductile cast iron has spherical graphite "nodules" which stop the crack from further progressing.
4. From the web site
https://en.wikipedia.org/wiki/Ductile_iron
Ductile_iron Ductile iron, also known as ductile cast iron, nodular cast iron, spheroidal graphite iron, spheroidal graphite cast iron[1] and SG iron, is a type of graphite-rich cast iron invented in 1943 by Keith Millis.[2] While most varieties of cast iron are brittle, ductile iron has much more impact and fatigue resistance, due to its nodular graphite inclusions.
Since ductile cast iron was not patented until 1943, obviously the cast iron brake drums made by Ford starting in 1931 were not ductile CI but grey CI. Thus the Mel Gross drums are equivalent to the original CI drums provided by Ford prior to 1943.
I encourage all to get the facts straight and you will then make the best decision.