Tom,
HANS wont work because it uses the two shoulder belts as part of the system. I think the same with the Hutchins, it uses an attachment that connects to the lever lock in a 5 point harness. An option may be the Simpson D cell. It looks like a parachute harness and uses the drivers thighs and lower torso to control head movement. My son uses the D cell in his minicup car and wears it over the standard neck brace. One thing to remember though is when fitted properly you only have an inch of head movement to either side. In mini cups we are allowed to use a radio system so that i can let him know where other cars are until they get into his field of vision. If you want to see one up close let me know next time you are up near IMI, I am only a few minutes away.
Here is safety soltions web site, they offer the D Cell and Huthins
http://www.hutchensdevice.com
Hans device site
http://hansdevice.com/site/index.html
Ken