[Model51]

On the assumption your "36" is a car, Kube is correct in that all production car engines in 1936 came with aluminum heads. The 40-6049/50-B heads were available for flat-topped pistons as service replacements for the production aluminum versions.

The cast iron 40-6049/50-B were the standard production heads for trucks from 1934 through 1936, so they are correct for those vehicles.

The embossed date tags indicate the heads are made as service replacements. Mid-1930's production heads made by Ford do not have date tags.