Hey Charlie

Not advisable.
It could result in overloading the amp and in the case of valve amps popping something like the output valves or tranny.

In ss amps could rrsult in overheating and then kaboom..

Here is a decent article where it was dumbed down enough for folks like me to kinda understand it better

http://www.prestonelectronics.com/audio/Impedance.htm

Cheers

Not a good idea at all... although you might get away with it at low volumes, you do run quite the risk, which is not worth it with a cool amp like you have.
If you're going to mismatch a tube amp, rather do it with the speaker impedance on the low side; the higher the speaker impedance, the more volts the tube has to see to get the same volume. Volts are what breaks tubes and output trannies.