Bill Porterfield did just this about 15 years ago with a carefully rebuilt engine from ZL1 #26.
All accessories, production 375.7 HP
exhaust manifolds, Camaro
chambered exhaust system,
36 degrees timing
As above with 2-1/8" headers 418.9 HP
replacing the manifolds
Air cleaner, alternator, AIR 447.2 HP
pump removed
Carb re-jetted, timing set 444.2 HP
to 39 degrees
Chambered exhaust system 523.6 HP
removed
Note the chambered exhaust system everybody craves cost almost 80 hp.
http://www.camaros.org/copo.shtml