I did a search for making wing tube sockets and I found this guy's website. Check out this link to this page showing him converting an O.S. 1.40 head to a dual plugs. He has some other neat "how to's" on his site also.

[link]http://home.online.no/~ofremmi/HowTo/Dual-plug/converting_to_a_dual.htm[/link]