Hank and KS,
Yes I heard same about the Pontiac OHC-6, as I heard it those Qjets had a very stiff air valve so that where rated (std 1.5" Hg) the air valve was still partly shut, on purpose, so they did not flow the normal Qjet 750cfm but rather only 650cfm.
I've not heard of a 650cfm vac sec Holley, just a 600, then a 715cfm downleg (excellent carb) first used in 1963 on the 427 Ford.
I think the 650 Double Pumper is still a straight leg booster like the 600 Vac Sec, and the added 50cfm of air is likely not needed. To get dogleg boosters you'd have to go to a 700 double pumper or the 715 vac sec.
So if the 650dp didn't run as good, it is likely coming down to which carb the engine "likes" better. If it is happy with the 600, that is probably the one to go with.
I think you could do an entire dyno weekend just dialing in a carb to a given combo. Then, if you changed cam, intake, or headers, it would no longer be optimum. All you can do in a short weekend is have a carb that all the combos are fairly happy with and show good AFR. I don't envy Tom's rushed task, it is easier for me to sit here and type.
