Your second round of photos look to be from the July 1966 races-#17 Charlie Kolb-Porsche 906 (winner), #21-George Avent-Lotus 23, #77-John Lewis-Scorpion (Troutman and Barnes Scorpion)...etc.
In agreement with rockhouse66-#18 GT350 is the Roger West 5r538 R-model at Daytona 1967, not Sebring (#18 for Sebring 1967-is the Dos Caballos Van Beuren GT350 R-model 5r108).