If the tubes for the A.I.R. are "turned down" into the head pipe (away from the valve), a slight gain in scavenging is achieved. It creates a "low pressure" area ("lowER" is probably more accurate) in the exhaust port. I recall a set of Hookers on a '70 or so Camaro done that way.
"Out of the box", Hooker is the best. Period. Buy them "painted" and send them to a REAL coating shop for a thermal barrier. We use Thermal Tech in hopewell, VA. Jet Hot (TX) and Swain (NY) also come to mind. The thermal barrier ios far superior to the ceramic coatings applied by header companies.
Your 601 heads "modified" are ALMOST as effective as a good pair of 441s or 993s. We've learned through necessity, "flow trumps compression". That is, while compression DOES "make" power, flow makes more. A good pair of heads with 2.02s (properly installed) will produce more power than 1.84s with two full points MORE compression, and be much miore pump gas "friendly".
1 5/8" primary, 3" collector is just right for this application. the 1 1/2" tubes would be okay, too, but no "room" for the future. Keep your exhaust 2 1/2 or smaller.