Need some carb selection advice

[sniper]

Hey guys, I am wondering if any of you could assist me. I don't know a whole lot about carbs and how to select the correct size.

Here is the deal, the motor is in a 66' F100.
It has a built 460 with 11.5:1 comp.
The motor is set up to run upwards of a 500 shot. But plan to maybe do 250 possibly two stageing it.
It currently has a 750cfm edelbrock. The guy wanted it to just run out of the box, so that is what he purchased. And it did what he wanted it too.
I believe these are the cam specs;
-Basic Operating RPM Range: 2,000-6,000
-Intake Duration at 050 inch Lift: 230
-Exhaust Duration at 050 inch Lift: 230
-Duration at 050 inch Lift: 230 int./230 exh.
-Advertised Intake Duration: 280
-Advertised Exhaust Duration: 280
-Advertised Duration: 280 int./280 exh.
-Intake Valve Lift with Factory Rocker Arm Ratio: 0.530 in.
-Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.530 in.
-Valve Lift with Factory Rocker Arm Ratio: 0.530 int./0.530 exh. lift
-Lobe Separation (degrees):

On the Dyno it made around 470 ft lbs at 4200 but only 298 HP and then the HP nose dives. And goes rich, If I remember getting to 12.1:1 or so on the wideband right where the drop off occurs.

If all that makes sense here is the question. I suggested that he go with a 950cfm carb, in either a proform, or holley. But I am not exactly sure (again not a carb guy) if that is too much cfm or if something else, smaller in the 850 range, would be better. Maybe a good quality, flowing 850 would be plenty, compared to the current low buckl 740 that is on there.

I hope that is enough make informed advice easier.

Preciate it, Mark.