To all concerned about Cox plugs. Yes, get a Galbreath head and Nelson plug. This will fit Cox AND Norvel .049 and .06. Norvels plugs, which, for the time being are also hard to get.
However, if you take a little care and with a bit of practise, you CAN make, from old Cox heads, a piece that will accept turbo plugs. These are similar to Nelsons but can be had in many more heat ranges from multiple suppliers. They were invented for the car engines and are claimed to provide a power boost. In any case, properly done, they will retain the power you had with your original Cox or Norvel plug and in some cases give you added power due to matching heat range with your particular application.
See how that's done here.
http://www.rcuniverse.com/forum/m_45..._1/key_/tm.htm
For Cox .09 throttling. If you can get the plastic, front carb body from a TD .09, you can add a throttle from an MVVS .09 available from Carlson Imports.
That's pictured below. The muffler is custom made by myself. The MVVS throttle needs the bottom stem threaded to suit the TD body and is simply JB Welded in place. The excellent thing about the MVVS throttle is that it has the very necessary, adjustable airbleed already installed. The engine pictured is a TD .09,,, don't know how well it would work with the Medallion .09 as it has a round intake port as opposed to rectangular one as in the TD.
I've converted an old head to take a turbo plug but this arrangement is yet to be tested.