the p3's and 412 p had the same 4-liter block which is different from the p4-4 liter block and all had p3 not p4 chassis. all of the p3 chassis were made in 1966 at the same time but because of labor strikes only three of the five p3 chassis were built up into cars in 66. the unbuilt up p3 chassis were eventually build up into 412p 0850 and 0854 in 1967. p4 0846 was unique having, after modification by ferrari for the 1967 race season, a p3 chassis with a p4 engine.