I don't think it's useless, the scale goes from 32F to 482F.
Plus it adds that boneyard, cold-war cool! All he needs now is an "eyebrow" or "post light" to illuminate it at night.
Also, it's a hell of a lot cheaper than a TSO'd, or even experimental grade version.
http://www.wpafb.af.mil/museum/outdoor/od17.htm
VDO makes one also, if you really wanted to you could have North Hollywood Speedometer silk screen a "Green Arc," "Yellow Arc" and a "Red Line" on the gauge, depending on the specs from your particular model.
http://www.nhspeedometer.com/cockpit_page1.htm
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