V-1710F from P-38 with P-40K, M, and N style of distributor (mounted at
the back of each valve cover). Distributor used on the P-40K (V-1710-73),
P-40M (V-1710-81),and P-40N (V-1710-81, -99, and finally the V1710-115). F
series always had the reduction gear shown here.