Have you tried talking to Clifford or Patricks?
I haven't used one, but it's my understanding that the newer style ones for water heat will not work with fentons, not sure about the older style. As for carb, a small 4bbl like a 390 Holley, or a small WCFB or Rochester square bore might work well. A 2GC 2bbl from a 283/307 could also be used.
A properly setup 2X1 setup will perform similar to the above 4bbl setup. It's mostly a question of what do you want it to look like when you're done, and how much you are willing to monkey around with carbs.
As for leaks around the bowl on a 1bbl Rochester, try using a new gasket and use a VERY small amount of Hylomar sealer on both side of the gasket. You want to avoid alot of squeeze out. DON'T use silicone.