Losing my tether with FreeNas - installing packages

[JC]

I am trying to install packages on FreeNAS 0.7.2 amd64 embedded.
Multiple guides & scripts have been followed but I'm always getting the error: pkg_add: can't stat package file 'python26-2.6.4'

It seems to be well documented that certain temp directories must be created first to workaround the 'embedded' install limitations, however I believe followed all the steps.

cd /mnt/Local
mkdir extensions
cd extensions 
mkdir var
mkdir usr
mkdir tmp  
mount_unionfs -o w /mnt/Local/extensions/usr/ /usr/
umount -f /var
mount_unionfs -o w /mnt/Local/extensions/var/ /var/
setenv PKG_TMPDIR /mnt/Local/extensions/tmp/

So installing packages I've firstly tried:

setenv PACKAGESITE "ftp://ftp.freebsd.org/pub/FreeBSD/ports/amd64/packages-7.3-release/All/"
pkg_add -rv python26-2.6.4

= pkg_add: can't stat package file 'python26-2.6.4'

Failing that I've downloaded the files manually and tried a local install:

hpbox:/mnt/Local/extensions/tmp# pkg_add -f /mnt/Local/extensions/tmp/python26-2.6.4.tbz

New error: tar: +CONTENTS: Not found in archive
tar: Error exit delayed from previous errors.
pkg_add: tar extract of /mnt/Local/extensions/tmp/python26-2.6.4.tbz failed!
pkg_add: unable to extract table of contents file from '/mnt/Local/extensions/tmp/python26-2.6.4.tbz' - not a package?

Any ideas where I'm going so badly wrong?