So, after getting the crossover tweaked manifolds from Needswings, I checked in with this thread and appreciate the pictures 180! After carefully looking at the pics and then the interface between the breather cover and the filler extension, it seemed clear that the filler neck stops were designed to just "ride" over the mounting stops on the engine. So, I got a pair of large channel locks, put a bit of cloth in the jaws to avoid scratching the filler neck, and gently but firmly rotated the filler neck counterclockwise. Came off like a champ!! easy peasy. Replaced the leaky oil filler cap gasket, and then put the cap directly on the breather cover. No more leak :-)

This was my experience. Your mileage may vary LOL.