Heads and a new intake manifold will be needed. Choices for EFI intake manifolds are limited, but in looking for a manifold setup for my future 408 stroker build I was thinking of Either the TrickFlow 351 R-Series Manifold or the Professional Products Typhoon Intake system. Both make power in the 1500-6500 RPM range. The stock manifolds are horrible and must be eliminated if you want to make big power.