Those manifolds are based on the late '60s design. Hard to compare to a later model Performer. Those end carb's plates were also drilled and rejetted by the super stock guys, right out of the box, as seen in the older Mopar Engine books. Those Carbs are probably set to the "rich&safe" jetting right now. That's why the dyno session with air-fuel mixture and exhaust temp readings would be the next step to help pull more HP to outperform that 870.
My friend with a 440-6, 70 Cuda jumped on it to pass a car on the Power Tour. He probably thought it was running great, but from behind, I saw a big cloud of black smoke. We all know that almost lean and almost pingiing puts out the most HP.
I also had a 6-pack, but as you saw on my car, I'm back to a 4-bbl air gap type manifold. I'm running a 1000 cfm air valve and yes, it is easier to tune. If I ever run a 6-pack manifold again, it will have (3) 2bbl throttle bodies on it. those Holley end carbs need those screw in jet plates to make them tunable. The original jet plates with the drilled jet orifices were a pain in the butt.
