318 combo

If you're looking at aftermarket cylinder heads my first choice for your build would be the EngineQuest Magnum heads. They are intended as new factory replacement heads but feature improved ports and extra metal in key areas for strength. Only $900 a PAIR assembled from Competition Products. They have LA-style intake manifold bolt pattern but require Magnum pedestal rockers, which would probably be an upgrade for you with the 1.6:1 factory ratio over 1.5 (actually less) of stock LA's. These heads are also known for lots of low-lift flow which is what builds torque esp. on the bottom end.