Not sure for this class (GT3). There are two prototype classes that usually have no road-going examples. The racing versions of production cars are no longer very similar except for basic appearance. The chassis and bodywork are often carbon fiber, custom suspension and braking. Surprisingly, the engine output is often restricted below the HP of the road cars in this racing series.
Thanks. I remember Ford sold 50 GTs but they all came with the 289. I thought that was cheating a bit but it must have been by the rules.
I guess Ford simply listed two engine options, the 427 or the 289. Of course no one would have willingly chose the 289 but they had no choice.