I am using two W-1 Carters, they work great for my 250 engine.
What ever you decide to use, they must be identical in number and metering. Don't assume over the counter replacements are the same, they are some of the worst carbs to use since the rebuilders use any part that fits.
Pick up cores for cheap and rebuild them, that way you know what you have. Also, run them together, don't try progressive linkage, one end of the engine will always run lean if you do. My W-1s are small by them self, but together make the perfect size for a 250 ci.
Joe