I think one way to tell if they are 340 manifolds is to measure the distance between the bolts where the pipe bolts up. Mine are right at 4 inches between the bolts where some 273 manifolds I have measure 3.5. Funny thing about the 340 manifolds is the passenger size outlet is smaller than the drivers side. That's why others are running the Dakota magnum on the passenger side plus they just look "swoopier"
