They are cleaner and leaner.
Who knows why Chevy in the 50s switched to Rochester Bs in favor of the better engineered Carter YF carbs.
They had custom designed versions for several models and years.
http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=2;t=007211#000000
......the NAPA universal manual choke conversion kit is about $20 or so.
