Not just that, the 76 Formula hood goes with the single round headlight fronts of 70-76, the 77-81 hood goes with the square double headlight fronts. The nosecone matches the hood front and headlight format so you can't swap between early and late without changing the front end.
The 76 scoops are almost half way back and rounded. There is no confusion with original fitment, only front end swaps.
Bugger it, links...
70-75 style Formula hood:
https://express-images.franklymedia....rd-Formula.jpg
76 Formula hood:
https://i.pinimg.com/originals/3c/34...098488189e.jpg
77-81 Formula hood:
https://img.hmn.com/fit-in/900x506/f...la_01_1000.jpg
A 79-81 hood also has retainer holes for radiator support seal, 77-78 plain.