I have one of those castings. Their name is on them because it is part of the mold. They were released because they are slightly warped and more trouble than they are worth for a manufacturer to deal with. For a hobbyist, they are fine.
The casting are already tempered. You will need carbide end mills, and cutters to machine them. The "special" cutters that you refered to are called woodruff cutters. They are common and not hard to find in most larger cities with machine tool supply companies.
There is a member of FALFILES that did machine one of those castings and did an outstanding job. It has been a very long time since he started a thread and posted pics of his progress. I don't remember his name or even if he is a current poster there. Ask around over there. I am sure that somebody remembers who it was.