[Crossbreed383]

Have you actually done any measuring to see if a carbed LS will fit under a stock Nova hood?
I can tell you a dual plane Gm manifold, on a aluminum Ls3 ,mounted as low as possible( aftermarket shallow front sump area almost touching frame) , using custom engine mounts, along with a L88 drop base air cleaner just barely fit under hood.
There was zero room for any sort of spacer and you needed to run a very short air filter element as well

Amazingly, a BB Chevy in the same chassis, a RPM Airgap, with a 1/2 Nos plate and drop base filter, fits with room to spare!

Good luck