Thank you for the write up, Todd.  I'm working on a Corvair engine, and want to get away from CHT probes with spark plug rings.  What I'm looking to do is have a small ring terminal clamped to the end of TC wire and then clamp that to the side of the head with a screw into a hole tapped into the head near the spark plug.  At that point, I'm picking up the temperature of the aluminum near the plug, without the probe being part of the spark plug installation.

The only question I have (and why I haven't moved forward with the idea) is, "Is it ok to ground the end of the TC wire?"  Your write-up seems to suggest that it is.