[prostreetC-10]

Correct on the carb size. The first circut is the same whether it's a 600 or a 950. It's not the jetting. It's in the transition from your idle circut to the main. This is where Holleys can be tricky. It's that "part throttle"...when the blades are coming off the transition slots. Once again, was it new when you put it on? The power vavle could have a little to do with it. They come with 6.5 hg vavles which usually is good for the "majority" of applications. If you have a little time, I'd find the Holley DVD on You Tube that comes with all their carbs. It's a very good DVD. Might not be a bad idea to just go over the adjustments and mainly to check the throttle blade positions.

One last thing on the dizzy. We might have the same ignition setup. I'm running the 85551 dist with the 6AL box. I'm not sure if SBC are the same as BBC but my motor loves at least 18* initial. I started around where you are but really smoothed out down low when I threw another 6* into it. Do you remember what springs you have in your distributor? I initially put in too light of springs and the advance was coming in when you breathed on the throttle. I bumped the curve up to hold the advance until around 1,800 and all in a little over 3,000. It made a huge difference on my low end stumble. You need to at least start with the carb though. Should be too hard to get the stumble out if you re-check the settings.