The newer motor is an improvement on the old, just like the 426 was an improvement on the original Hemi. I'd take a modern SRT 6.4 in my muscle car over a 65-71 426 anyway.
No, not in the design of the combustion chamber. It is actually a step backward. The only "improvement" is all of the electronics and computer control. The new Hemi head is really not a Hemi at all. They simply used the name.
