Distfiles mirror behind proxy

[Max Asato]

I'm looking for info and seasoned advice on getting MacPorts to work
for a moderate number of users (probably less than 50) behind an
authenticated http/ftp proxy.  We already provide an internal mirror 
server for CPAN, CTAN, and a bunch of Linux and BSD distributions so 
hardware and expertise in setting a mirror up for MacPorts would not 
be a problem.

Rsync to external servers isn't permitted from user desktops so
I've done a bit of testing with MacPorts 1.6 and have been able to
get the sync and selfupdate functions to work with an internal mirror
of the ports and source trees.  We'd have to customize the macports.conf
and sources.conf files in the installer but that seems to be workable.
Any other suggestions?

We would ideally like to mirror the primary distfile server internally
as well, but it sounds like that the new distserver.macports.org site
is tied to the 1.7 release.  I've futzed around with the mirror_sites.tcl
file a bit so it looks like it would be possible to direct our users
to an internal mirror first before trying to navigate through the
proxies.  Are there any reasons not to do this?  It looks like the
MASTER_SITE_LOCAL environment variable mechanism doesn't support
subdirectories under 1.6, does 1.7 work differently?

Last but not least, is there any way to get MacPorts to install packages
from a port archive file that was built on another system?  I've set the
portarchivemode parameter in macports.conf on two intel Macs (both
running 10.4.11), built a package on one and copied the archive over
to /opt/local/var/macports/packages/darwin/i386/ on the other but
MacPorts ignored the archive and attempted to fetch and build the
package again on the other system.  It would be nice if we didn't have
to subject every Scipy user to a bootstrap build of gcc.

TIA,

-Max