Porsche used its Rennsport Reunion gathering held last week at California’s Laguna Seca racetrack to present a 718 Cayman RS developed in partnership with Tag Heuer. The car celebrates the 70th anniversary of the running of a pair of 550 Coupes in the 1953 Carrera Panamericana, and just two will be built, one for each of the 550 Coupes that…