Beach Boys and Whitman 'met' once via Brian & Kalinich' poetry album: A World Of Peace from where Leaves Of Grass is based upon a Whitman poem
(according to Andrew Doe). I suspect that Mr. Hattesen wouldn't know about this connection - not until september at least.
"Leaves of Grass" is the bonus track on
A World Of Peace Must Come - produced by Carl for Stevie K's band at the time (1968), Zarathustra & Thelibis. Not truly a part of the album.