Do dual exhaust manifolds for the 330 exist? Thanks

 

There have never been true dual exhaust manifolds for any small block Olds from the factory, except those used on Toronados in the late 1970s. The Toro manifolds don't work in a RWD application as the outlets point the wrong way. Even the W-31s got the normal manifolds with the cap on the crossover port on the passenger side.

There are aftermarket manifolds available that have this port blanked off. I suggest you carefully compare them to stock and judge for yourself if they are worth the considerable cost. Contrary to some claims, these aftermarket manifolds do NOT have internal runners like the BBO W/Z manifolds. There just isn't enough room with the the SBO to do it.

 

Basically you cap off the crossover and run your dual exhaust. You can either buy one from a multitude of resto vendors and ebay (see pic below), or make one yourself.