OK as promised here's a pure 64-bit Cocoa based build. It runs well in my 64 bit Leopard VM, so keep your fingers crossed...
I should note that I had to make lots of changes and over 3000 lines of new code to build the 64 bit version. Plus all of calibre's bundled dependencies have also had to be compiled in 64 bit versions, and believe me, all of them did not go quietly, so I don't expect everything to work out of the box. Treat this as a beta release.
http://calibre.kovidgoyal.net/downlo....10-x86_64.dmg
Phew!