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Just be careful when you gonna test your amplifier. Avoid overloading the amplifier (clipping) and parasitic oscillations. I ruined 3 tubes during tests ((( A good protection mean is to connect a lamp in series with the amplifier's power transformer primary. In case of any parasitic oscillation will protect the tubes...hopefully! Of course if everything is ok you will need to remove the lamp to drive the amplifier at maximum output. An oscilloscope is a very useful piece of testing equipment.

Why not just figure the power into a 32 ohm load and use an RMS meter to tell you the voltage? Won't this work using a scope to tell you when clipping occurs?

Voltmeters cannot tell when clipping occurs but oscilloscopes can, therefore I always use it because I can see if the output signal is distorted, unsymmetrical or whatever else that is not normal .