Correct me if I am wrong, but have to be seven and seven. Air cooled radial so it can not be other than seven and seven. Can't divide it any other way. by the way the Zero was a copy of the T6 Texan, a trainer by the way. The Japanese bought a few of them in the thirties and copied them. They used Texans in the movie Tora Tora by the way. Had an old WW11 vet exclaim once that those were not Zeros but Texans during showing of the film. 18 cyl on the Douglas would have to have been three rows, I would guess. The Japanese left out all the armament and other things to give the Zero the climb and speed. Too bad so sad, the F4's and F8u's chewed them up so very badly. Bill