Between 1992 and 1994, Porsche Motorsports Research and Development built and provided a full "Race" version (stripped out 968 Turbo S) for Porsches customer race teams. The 968 Turbo RS was available in two variations; a  version using the K27 turbocharger from the Turbo S, which was built to the German ADAC GT specification (ballast added to bring the car up to the 1,350 kg minimum weight limit), and an international spec version which used a KKK L41 turbocharger producing  and was reduced to 1,212 kg in weight. Only 4 were ever produced ; 1 Guards Red (WPOZZZ96ZNS820065),  1 Speed Yellow (WPOZZZ96ZPS896061), 1 Black (WPOZZZ96ZPS896062) and 1 White (WPOZZZ96ZPS896063). These are the rarest 968s ever produced.. How many years did it take for Porsche Motorsports Research and Development to build and provide a full "Race" version for its customers?