PQR,
Your Fisher will work with any of those tubes but if you don't use 7189s the life of your output tubes may be shortened. A couple hours or a couple days or even a couple weeks will probably be Ok. But you'll be hunting for tubes in a couple months minimum and a couple of years definitely.
That being said, NOS JAN 6BQ5s are probably close to being ruggedized enough to be considered a 7189.
In my X-100-3, I've experimented with a ton of 6BQ5s, though it calls for 7189s, but I've settled on Sylvania 7189s over the Tele and Ampx 6BQ5s.