The only carburetor I'm aware of that was specifically designed for a 261 was a Rochester B with a slightly oversized venturi to accommodate the extra displacement. Those carbs are scarce, and they have a host of design problems that haven't gotten any better with age. Try to find a Carter YF calibrated for an AMC/Jeep 258 cubic inch six. It will have the same manifold stud spacing as the Rochester, and it's a much better design. The 292 carb would run pretty lean without some major rejetting.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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