I'd never paid attention to it, but after taking my intake off today I see that it has two PCV valves installed, on on the valve cover and one cover below the intake (intake valley pan?). Both run to a port on the intake, just in front of the carb. 67 firebird supplement shows one setup using the valve cover and one using a valve behind the carb I think.

Any reason that there would be two installed? If it matters, valve covers are the sealed type (no breather).