Well, mostly, you can purchase new plugs for the galbreath head.

THe following is information on the two aftermarket heads and plugs verses the standard #325 cox head.  I have never tested them verses the high  compression TeeDee head

You will gain a slight amount of RPM with the Galbreath and Nelson plug or the stock head, about 500 to 1000 RPM
You will  loose a slight amount with the Mecoa glo Bee head, around a 1000 or slightly more

The difference is how and where the plug seals to the head.  The Galbreath/Nelson seals at the bottom of the plug and this makes a slightly smaller combustion chamber and higher compression.  The glo bee and plug seal at the top and this will also include space around the threads and you gain combustion chamber but loose compression.  IN such a small displacement engines just a little makes a big difference.  Hope thisis what you where looking for.  Your mileage may very but I have video around on one of my old computers showing my tach readings.  I tried to be as consistant as possible between tests but I'm just a amature

       One thing to mention about Glo Bee plugs is that they're are two different types of them. I recently discovered this a few months ago. There is a Glo Bee racing plug which has the squish band almost identical to the Cox high comp head. Then you have the other style which I refer to the trumpet style. The trumpet style as I say has a hemi head as well but its smaller. The racing style leaves almost the same surface area in the landing leaving just enough for the shims to seat on. The other style has a much larger landing area and what appears to be a smaller dome area. I would say from my experience, I've had a handful of problems using Glo Bee heads in general. When they work, and I had them work great they're fine as far as performance is concerned. I would say I've experienced a bit more power out of them compared to the Galbreath Nelson combo. The problem is finding the correct amount of gaskets. The racing style as I mentioned seems to be the least compressive. The trumpet style which if you can get the engine to run will give you amazing performance until the engine overheats and sags. I've had to use as many as 7 gaskets when using that style. It seems almost unheard of. I just couldn't get the engine to start as it would kick and try and run forward then backwards as if the engine was idling. I've had them instantly blow though after it went into a screaming run. They're not reliable in my honest opinion. I would recommend trying them though cause if you can get it to work its impressive. The Nelson set up works very well but this may require 4 gaskets or more at times. All my testing has been with Tee Dee's on two 1/2 a speed planes I built. One still is currently using the Glo Bee which has been run hard on a regular basis. I just find the Nelson plugs to very reliable and take ground pounding well on my combat engines. I have shims for under the cylinder in which I add them .002 at a time which lowers the piston from the deck height which enables me to use less glow plug shims. This has been the only way I can get the Glo Bee heads to work correctly. I never had to do this using the Galbreath head combo. The Glo Bee uses a fairly large coil and I find this to get scrambled under hard runs and high nitro. I try to straighten them with a T-pin from time to time due to it bunching up and not glowing well. I've been using the Merlin plugs in which I drill out the Glo Bee clamp to hold it and these have been working well for me. I haven't blown any yet but they can be finicky with the gaskets as well. These take no less than 3 for me to work correctly. I like the Cox high comp heads but the cost is up there and they just don't hold up well for me at least. Ken

My Galbreath had is as good or better than a Cox high performance head.  I am still playing with shims un the head adapter.   

   I have used the Galbrath / Nelson plug combo. I have had no problems with this set up and regularly see a 1000 plus rpm gain over the standard Cox 0.49 head. I havn't tried anything else, as I just wanted to have a set up that was cheaper than the standard 0.49 head. I have used one gasket and find that fine. The Nelson plugs seem to be indestructable, so it is win win, cheaper plug that lasts and lasts plus a power increase.

Regards,

Andrew.