Cox glow heads are available but expensive. The only real problem with tapping for a standard plug is that it messes up the combustion chamber shape and you'll lose maybe 1500 or so revs but it's a good fix if top revs aren't a major concern. Norvel heads will fit in the Cox and are said to give more revs as well. The preferred cure nowadays though is to get a Galbreath head and use a Nelson plug. Go to https://ssl10.mysecureserver.com/kit...dex_store.html and click on Glow Plugs.

I'm not an expert on Cox engines but I'd read about all this over on SSW so I just did a search to find the information.