If you can find one of those carbs calibrated for the 55 Ford 272 V8, it will probably work pretty well on a 261/270 engine without much, if any rejetting. The 272 carb has a 1 1/16" venturi diaimeter and when I tried to use one on an overbored 239 engine (252 cubic inches) instead of the original 15/16" venturi carb it was slightly over-carbureted. It had a flat spot at part throttle. Other than that little problem it ran well, especially at full throttle. The gas flow through the manifold for a six is a little different than a V8, but the volume of flow should be similar. The "hobby" class race cars we ran with flatheads used those carbs very successfully.
Jerry

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