I used a 56 4 barrel automatic bellcrank on my 55 Ford Club Sedan, running a "B" intake, and I had to take off some material on the bottom of the bellcrank, but it works perfectly - I have "0" issues. As stated, a 57 may work if you change your fordomatic kickdown rod adjuster (that L shaped bracket on the top of the threaded end) to a clevis pin style like the 57's had. Finding these bellcranks can be somewhat tedious. Usually people want an arm and a leg, but it saves the hassle of fabricating something up if you don't quite have the skills or patience. Just letting you know the differences, that way you can have one more option than just the 55 or 56 style.
FYI - the original 55 4 barrel bellcranks are usually sold for quite a bit of dough - it is not unusual to see them go for over $100. But I have found 56 bellcranks for $25 or less.
Dan
Daniel JessupLancaster, California
aka "The Hot Rod Reverend" 
check out the 1955 Ford Fairlane build at www.hotrodreverend.com