The head of Fiat at the time, Gianni Agnell was the sole recipient of the one and only Testarossa Spider built by Ferrari. After many requests for more to be built Ferrari declined to oblige. So Pininfarina and other firms cam to the party to produce unofficial version of the Testarossa Spider.
The mechanicals were no different to that of the regular Testarossa. Apart from being a convertible, the only other differences between the two cars were the front window and doors being shorter on the Spider.