Generally, a four barrel on a six would be mounted with the primary side toward the engine. I cannot recall previously seeing a carburetor mounted with the secondary side toward the engine.
If the manifold were designed for it, a better way would be to have the primary side toward the radiator, as most 4-barrel carbs are designed for mounting in this manner. Depending on the design of the carburetor in question, fuel slosh can be a problem when rotating ninety degrees to mount on an inline six.
Jon.
