ORIGINAL: The Flying Farmer
In order to maintain integrity, I opted to grind down a glow plug wrench instead of the adapter.
Mine is from Gene Barton. His adapter puts the bottom of the plug flush w/ the cylinder, thus the need to grind a wrench.
http://www.genebarton.com/accessories.html
A nut driver (Spintite) is easier to use and can be ground down to a thinner wall than the typical glow plug wrench. I think it is a 3/8 inch size. I use a nutdriver also to loosen/tighten the hex heads on my nylon wing bolts.