ATK 5.9 Magnum crate motor horse power

The CH318A and B are the exact same head with one difference: the A is tapped for the Magnum-style straight down intake manifold bolts and the B is tapped for the original LA-style 45 degree angle. (As you said, the second letter (AA and BA) just means assembled w/ valves & springs.)

The EQ head was an aftermarket replacement head but they were smart and made it flow more while they were at it and made it to be tapped with either style intake manifold. Very smart on their part. (Not sure why they sometimes called one Performance; they were inherently higher performance from the start.)

I looked at the EQ318 and JEGS head side by side (below). Now I'm not so sure. There are definitely casting differences. Does JEGS really make their own head?

EQ-left-JEGS-right-heads