Is that so? Even in the book I read, it is written as ''if he be.....'' I don't get why it is not ''if he''ll be....''
sounds more like "if he is" to me. it takes context to extract intended meaning from purple prose. perhaps this is an expression of the 'voice' of a particular character. writers use all sorts of forms for all sorts of reasons, and the cultures and times they live in are an influence too.
I believe my friend the esteemed Cannabis Poet of Amsterdam would say that the writer was using his "poetic license" to say something that might rhyme with other word patterns.