The steel crank is the only one that has a completely smooth outside diameter rear crank flange. Also, one of the counterbalance weights will be marked C1TE. And, the first two counterweights are at the same angle relevant to the snout (like the first two 312 crank counterweights).
I have a crank listed on ebay right now with 2 photos if you want to search for it. There may be others.
Daniel JessupLancaster, California
aka "The Hot Rod Reverend" 
check out the 1955 Ford Fairlane build at www.hotrodreverend.com