The CNC ported chamber option helps low lift airflow substantially.

Our local cylinder head expert, stressed working the chambers on most BBC heads to me, years back. Guy is pretty sharp. Aside from the aid in low lift airflow, the swirl effect, and other tricks to aid in combustion efficiency were in his opinion, the best place to spend money on most bbc heads, aside from the valve pocket area, valve seat angles, and valve backcuts. He's old school, and has been porting bbc chambers for years, just doing it by hand the old fashioned way.

Myengine guy told me same stuff today also....

A few years back I took a set of aluminum Pontiac heads to Tommy Slawko. Told him to get what he could out of them. When I picked them up he never touched the ports he completely re-shaped the combustion chambers in the heads when he was done the chambers almost looked like a perfect heart shape. Just from doing the combustion chambers in the heads they picked up 30cfm. I asked him why he didn't touch the ports and he said they weren't worth porting if we wanted to get something out of them he would have to cut the heads up move the ports and weld them back together. There is a whole lot to a combustion chamber not just combustion it affects every stroke of the motor.