Hi,
I think most commercial adapters would be made in aluminium on a CNC lathe, a bit of an advantage to have. If you use aluminium it probably helps to know something of the big range of alloys, not all of them amenable to thread cutting.
http://www.globalmetals.com.au/_pdf/...um_Summary.pdf
You need to use a messy cutting oil as well for the best finish.
I think I'd use brass instead where possible, looks great, and the machining grades cut like a dream. It's 3-4x more expensive though.
As to the tools, you can grind them up yourself, or look at commercially available stuff like
http://www.carbatec.com.au/cutting-t...essories_c2490
Cheers