This is going back sometime, but Dunnuck was looking into doing some deep porting Six Pack testing. I think he fell of the face earth as I haven't seen him post in a long time?

Correct, however the boss is there in the main body and would require drilling. Take a second look at 68 Hemi GTS picture, its right there....

Well, this thread certainly has a variety of theories in it.

The easiest way to (roughly)compare two barrel and four barrel holley style carbs for flow capacity, since they are tested and rated at different pressures, is to compare the Venturi and throttle bore diameters.
For example, a secondary OE 6bbl carb has the same size venturi and throttle bore of an 850dp Holley # 4781. A 4412 is the same as a 750dp Holley # 4779.
In other words, when tested under the same parameters, 2 4412 Holley carbs don't flow 250cfm more than one 4779. The 2 4412's basically flow the same as a 4779....... Or roughly 375cfm when tested at the 4bbl pressure.

To the OP........ Compared to the stroker 6bbl motors I've tested, that jetting would be pretty lean. For the power levels you're at, we usually end up with secondary jets in the mid-80's.
I also agree that with 330cfm heads on a 11:1 shortblock and a 260 @ .050 cam you should have seen a bit more power. 650?? Who knows...... Dynos can vary a lot, but 610 seems like there might be some left on the table.

Just wondering where did you get two 4412's? The 4412 has a factory rating of 500cfm however they rated at, and it replaces the center carb.

Let me rephrase, do you think that a 4412 in the center would move more air than the stock six-pack center?

I was using the two 4412's as an example to compare to one 750 4 bbl.
The two 4412's equal the one 750 in terms of Venturi area and throttle bore area.
Does it seem logical that the two 4412's would flow 250cfm more than the 750?

Does a stock 6 pak center carb flow more or less than a 4412?
Look up the Venturi diameter and throttle bore diameter for both, then you tell me.

The stock center for a 440 is a 4144 carb, it has a 1.187 venturii and a 1.5 throttle bore for 350cfm. The 4412 has a 1.376 venturii with a 1.688 throttle bore for 500cfm. So I say that the 4412 moves more air. This was from Holley's web sight.

ayye aye cap .. love my Lm1 and 2 great to have these tools today .

Yep, my junk was runnin low 10`s till I chassis dynoed it w/air fuel capabilities then right into the 9`s............invaluable tuning AID not end all but a directional tool......

the "real" 6bbl flow numbers were 250cfm center and 390cfm for each end carb. venturi area is a little over 9.8sqin's. i don't get overly lost in cfm numbers because they're manipulated, but you can't lie about venturi area.