the code for the plan 9 kernel for the SGI Challenge-M
(and relatives), which would simplify doing an Indigo2 port,
isn't included in the distribution
because it relies on information obtained from SGI under
non-disclosure agreement.  much of that data will now
be available more generally, since i think there is a Linux
port to several older SGI platforms, but unfortunately even if true that
in itself doesn't free embattled debt-laden telecommunications
manufacturer Lucent from the original agreement unless SGI agrees.
you could try finding someone in SGI who can agree to it.