The serial number indicates it is a 1928, which normally would be a K-40, and since the serial number on the block is the same I’d say it is a 1928 K-40, but like someone said earlier the smooth manifold edges indicate the K-35. Maybe someone replaced the manifolds??? Maybe Johnson was using up old parts?—But the serial number is not early 1928, so I’d guess they used up all the ’27 parts by then and what you have is a K-40 with K-35 manifolds.
George