I think a Quadrajet would work well here, they will flow 750cfm but act like a small carb until they need to open up. The mixture settings aren't too hard to adjust and the float bowl is in the center so you can mount it sideways with no trouble. You will be able to keep the same carb when you upgrade everything else. I used one on my Buick 225 motor in my Jeep and went through several intake and exhaust upgrades and it only needed minor adjustments.
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1950 Chevy pickup with '62 261, 4 speed.
