The 6.4L is based off of the 2009 or newer 5.7L Hemi and the manifold would bolt up. If your Hemi is a 2008 or older, the 6.1L manifold should be a direct bolt up, but I'm not sure if the 6.4L manifold will fit the earlier Hemis.
Regardless of fit, the 6.4L manifold has a solenoid actuated short runner valve (SRV) that changes the effective length of the intake runners depending on engine RPM. You would need to find a way to actuate this valve at the proper RPM or you wouldn't be getting much benefit out of the swap.
'06 Rubicon Unlimited
Sienna Jeep Club: Member #15