Looks like you need to post on a Firebird or Cutlass (442) site. It would make sense that a black jar made by another GM division could fit your bracket. I think that bracket dates back at least to 62 for most Chevrolets. But I will tell you, Classic shows a white jar on their online Firebird site. I did find one parts company, oldmusclecars.com, that does offer a black jar as "optional" for 67 Camaro.
Are you planning to show your car?
...When you stop to think about it, a black jar looks (or blends) "better", when you open up the hood. Although, at a show, when you see that white jar filled to the top with blue washer fluid, it sure "looks original".
BTW, the original part # for the washer jar is 3840083.