Probably the only way I can determine what I actually have is to buy a 1974 GM parts book and see what actually came stock (or was available) on a 1974 Nova, and see what these drums were available on AT THAT TIME. In the ensuing 45 years since this car was built, I'm sure these drums have been retrofitted to many 3rd Gen Nova and Camaros, but I am pretty sure that back in 1974, these drums were something special on this car. The fact that Harry Hammond, the engineer who built this Nova said that these were special parts on this special car indicates that they were probably special parts on this special car.
This drum is what SS396.com says is the 68-74 Nova rear drum.
https://www.ss396.com/nova/FBD-95R.html