[HardcoreZ28]

Dave,
Does the brass looking piece thread onto the steel collector for the AIR tubes? If so you can probably get the bronze piece at a junkyard for cheap and either get the air diverter valve there or they are still available at parts stores I believe. If it's not threaded on you may have to get a set of air tubes off an old manifold and cut the fitting off both pieces and tig weld it onto your manifold...or get a junkyard manifold.

I really don't remember how that piece is on there....I removed my stock manifolds soooooo long ago.