I found these 6.4 engine specs in the March/April issue of MOPAR:

4.09 Bore
3.72 Stroke
10.93:1 Compression
470 hp @6,000 rpm
470 torque @4,200 rpm
2.13 Intake Valve
1.65 Exhaust Valve
Active intake FI induction system (composite intake manifold)
Variable cam timing (allows movement of 37 crankshaft degrees)
Multi-Displacement (MDS)
6.1 Exhaust manifolds
Larger water jackets than 6.1 to improve circulation around bores
New oil squirters
New oil cooler to reduce piston temperature
Thicker cylinder head deck for structure and larger water jackets
Smooth core technology cylinder heads (like Viper)
Casting cores use same smooth FS90 sand as the Viper
Larger diameter valves have "tried and true" cooling technology
Exhaust valves are sodium-filled for temperature transfer
Valves are controlled with ovate-wire beehive valve springs

Note: The 392 has the best horsepower-per-liter numbers if any cam-in-block two-valve engine. (This includes the LS-7).