There are lots of good suggestions here about potential replacement carbs. Your Rochester B is probably a turd, as are most. I am a YF convert and will never go back.
However, I’d put carb shopping off until you shore up nearly everything else. Find and address vac leaks, get ignition and timing dialed in, get the valves properly adjusted, etc.
If you get those things right, your 261 will most likely run pretty respectably….even with a B. Then when you do upgrade carbs, you will appreciate the sweetness that a well-designed and well-tuned carb brings.
