The cylinder heads are extremely common and inexpensive 5.7L Hemi truck castings. The stock flow is a respectable 259 cfm at 0.600 lift, but they can be ported to 290 cfm or more with some work. The weak link from the factory is the intake valve seat that tends to drop into the cylinder. We’d fix that, if nothing else. Here you can see the “quench” chambers on our ’06 Hemi head. Hemi heads use two plugs to clean up emissions, not make more power.