That brass fitting (block) is different, for different years/models truck.

A truck with manual transmission has a different fitting/block than the one used on a truck with a hydra-matic transmission.

Most likely, there were different blocks on some earlier trucks?

Jim Carter & Chevs of the 40s & The Filling Station do not list any.

Maybe someone knows another vendor that has it/them.

What type of transmission on your truck?