Running 2 finals on a Budda SD30

I read somewhere, can't find it now, that you can pull two of the output tubes on a SD30. But I vaguely remember that you need to change the Rectifier as well for it to be well behaved when doing so. Does anyone have any information on what I need to do? Do I need to change the speaker impedance as well?

Or, if anyone has an SD18 1-12 combo they'd like to trade me... I'd take that too!

Thanks!