If your 383 doesn't have Vortec heads, it should be good to go. The air gap essentially keeps the runners up and away from hot oil splashing on the bottom of the intake runners, and heating the intake charge. Some engines already used that, like Pontiac etc. Chevys never seemed to have any trouble making HP with the old manifolds, but maybe the isolated runners adds some power (?)
I have an Air Gap #7501 manifold which I am going to put up for sale.It is just like a new one, has travelled maybe 500 miles. Contact me by PM if you have interest. Price would be $150.00 you pick up the shipping.I paid more for it, but I am always swapping stuff around. I have a dual quad setup I want to put on.