the Hurst T top started in 1976 . but there was 2 other Co. that made t-tops. also76 was the last year for the 455
here is a 75 with aftermarket top'* the tops look like 78-81 fisher tops. you can see this is a 75 because of the 1 year bumper grills with the running lights in the grill.
another type of aftermarket top
pic of a 76 50th w/Hurst tops