I saw this on sccoa yesterday and thought it might be of interest here. I am assuming the same principles would apply to a CV/GM electronic speedometer. This article basically shows you how to convert a 0-85mph speedo to one that reads 0-145mph (or whatever range you desire within reason). I have not tried it and I did not write the article.
http://www.sccoa.com/faq/SpeedometerConversions.pdf
http://www.sccoa.com/faq/SpeedometerConversions.pdf
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