Dan, I'm not familiar with Tempest plugs, but when I had my Lycoming O-145, I was able to remove the plugs with a standard box end wrench. I still have it. If you can use it, it's yours.
Awesome! I'll have to fly over and get it!
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Dan McCormack
Smoketown, PA (S37)
N24286, 1940 Aeronca Chief 65-LA (Lycoming O-145-B2)
CFI http://flightmusings.blogspot.com/