No, Gram didn't write the lyrics. Some fellow from Harvard did. it's all in Ben Fong Torres' book Hickory Wind (excellent book BTW)

No, the king with the "amphetamine crown" is a reference to Gram himself as I recall and not Elvis. I'll try and source that for you though. I once asked a friend of Chris Hill's to ask him for me and he didn't wish to dignify the question with a reply apparently being sick of questions about Gram. Still, I have a strong recollection of reading in several sources that it was a reference to Gram and not Elvis. The poem was written by a guy who was a fan of Gram's so it makes sense. Not a 'fan' in today's sense of the word, however.

Perhaps I read it in Phil Kaufman's book? (which has some nasty things to say about Polly's mother Nancy and Polly's paternity BTW, none of which i believe is true)