I think that's a small block shroud, not for a big block. As far as I know there are no reproduction injection molded plastic shrouds available for the 67 GS 400, only a fiberglass reproduction. So you have a Buick part there, just not sure it's the right one for your car.
This its is not for a 67 GS.. Ill get back to you with the exact measurements.. The 67 GS 400 does not have mounting tabs.. Hope this helps..
Go to post #2 to see a pic of a 67 GS shroud . The pic you posted only slightly resembles what the 67 shroud looks like. http://www.v8buick.com/showthread.p...0-fan-shroud&p=2294513&highlight=#post2294513