If you're in the US it's impossible to register any of the ROW cars unless they're at least 25 years old. So are you talking driving them on private roads, or trying to federalize it, if the parts are available to do so? Even with the parts and unlimited funds, the hassle and paperwork is a PITA, and you won't be driving the car for probably a year or more. Why not buy a nice Veyron and call it a day if you don't need carrying capacity, or pay Hennessey to convert a truck or SUV for you?