To further report the machine seems to be running after installation quite "snappily" though I seem to have messed something up and get a lot of messages about failed venti writes, due to a lack of a connection.

venti=/dev/sdC0/venti
or
venti=#S/sdC0/venti

in plan9.ini
not sure which is best, I have the former and it works but the latter was already in my plan9.ini and that didn't work but that might be something else and I've never experimented after it worked :)