I see you're listing Sigil as x86_64 compatible for the MacPorts version. I'm not sure that will work out-of-the-box. See
this page for details.
Basically, to work on x86_64, Qt needs to be compiled against Cocoa, not Carbon. I'm not sure the Qt version on MacPorts supports this. Have you tested this?
EDIT: The 32 bit Carbon version of Sigil should of course work without problems on x86_64 Macs.