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http://www.autospeed.com.au/cms/A_0717/article.html
The following video was shot on a frozen lake in Sweeden in Febuary 1979 and sees rally legends Hannu Mikkola and Bjorn Valdegard demonstrate two Group 4 versions of the classic in front of the assembled media.
Thirty examples were built between 1983 and 1986. In addition to numerous small component upgrades, the Callaway GTVs included a much revised suspension, larger brakes and a twin-turbocharger system, boosting performance to near-exotic levels.
The car's performance caught the attention of Dave McLellan, Chief Engineer of the Corvette, and would lead to the Callaway-Corvette association it became famous for.