Walt Whitman I think has to be an INFP. Song of Myself consists entirely of Ni style self-exposition, while has statements about how he has conductors along his body that "pass all things through [him] harmlessly," which sounds like the quintessential statement of P. Lilacs and O Captain, and especially (especially especially) the Calamus poems are VERY F. Super F. Power F. Read "We two boys together clinging"; I'm an ENFP, but if I read that poem with my "thinking" mindset on, I'm pretty sure I'd find it horribly sentimental. I know one might argue that he's E because of the "Rough Walt" and his extreme extraversion, but if one considers functional preferences, he seems to write entirely out of Ni rather than Ne. Everything is considered relative to Walt.
This is in contrast to Shakespeare, with whom everything is considered with as little relationship as possible to William, which is why I think his primary function must have been Ne, which would make him ENFP rather than INFP, but that might just be me attempting to claim Shakespeare for my own type. I'd say Shakespeare is definitely P (drama in London before Marlowe before was very overtly moralizing, and Shakespeare definitely latched on to the Marlovian revision of that trend). I'd have to say that he's F, I guess, but he's T is so well developed in his plays that it's almost impossible to say whether he's T or F. I know that he seems not E based on some biographical info, but I believe that trend resulted more from him being forced to be more J by circumstance (he didn't want to go the way of Marlowe!). Plus, the whole "fall passionately in love with Anne, knock her up, then get bored and move to London" seems like a real ENFP-type action. I mean, he couldn't even make up his mind about which lover to devote his sonnets to! (and wrote all of Sonnet 144-I-think about the real or imagined love triangle between the three of them).
I'd be willing to grant ISFJ for Heaney. He's a more tactile poet than most, excepting Wordsworth. I also read some of his poetics and it's more rules and less random Wallace Stevens-style abstractions, lending support to the S preference. Plus, I'd totally believe him as an SJ guardian, especially on the basis of "Digging," which has a clear confessional streak in it, and probably represents his life fairly accurately. Digging has a real "extend and protect the tradition" feeling to it, and the poems he wrote about the Catholic-Protestant conflict in Ireland has a very J slant to it, IMO.