"Robert Frost was on the beach this morning and is coming to dinner this evening." So did Wallace Stevens write to his wife Elsie in February of 1935 from the Casa Marina, a hotel on the Atlantic Ocean where he spent part of each winter in Key West for nearly 20 years. Frost and Stevens today are broadly acknowledged as literary peers, but in 1935 the two poets' reputations were leagues apart. Frost had won the Pulitzer Prize twice, while Stevens had published only a single volume…