The other thing to realize is that bare head flows are nice for comparison but actual intake CFM will almost always be lower with the intake manifold attatched. And the type of intake manifold makes a difference.
Conversely, while bare head exhaust flow may seem low, it will usually increase in actual conditions as scavaging will increase CFM if properly tuned. Scavaging can also increase intake flow depending on the cam overlap.
The C5R heads have a different shape port in a different location so you will also need a custom intake manifold.
The LS7 heads are similar but there hasn't been any confirmation yet that the intake ports are exactly the same as the C5R heads....so no one knows IF the new LS7 intake manifold would fit on the C5R head....but it might.