I've worked on a 9500 or two, and you don't need to worry a whole ton about the wattage rating of the dummy load, as there doesn't generally need to be signal going through the amp to set the bias. (If that 9500 has original power supply caps, it's absolutely mandatory to replace them, even if the amp passes signal)
The variac that I have that I like is an autoformer variac that can take in 120V and make up to 250V, but I don't see any available in the usual places. A 20A unit would be pretty overkill, but it's not insanely expensive.