Yes. You'd need an output transformer. The 2A5 output tube is equivalent to a 6F6 electrically. It likes to have a 7000 ohm load. Luckily here is a site that uses the 6F6 as an example, showing how to calculate the transformer needed to operate with a speaker of a given impedance.
http://www.radioremembered.org/outimp.htm
You may have a transformer in the junk box that will work. I wouldn't hesitate to try one as it should be OK for testing purposes while you're getting the chassis recapped. Then a universal transformer intended for a single-ended amplifier should work fine as a permanent replacement. On those you can choose the taps that work the best, by experiment.
Your resistor to take the place of the speaker field coil can be about 1000 ohms, 15 or 20 watt. You might get by with a 10 watt but the higher the wattage rating the cooler it's going to run. It would have to be mounted so it wouldn't overheat any other components. Once the set's working, you could check the plate voltage of the output tube vs. a tube manual and see if it looks reasonable, or if the big resistor needs to go up or down in ohms.
EDIT: just noticed that the NostalgiaAir entry for this set shows typical pin voltage readings for the tubes: with a modern DVM, your voltages will show higher.
OK, now I'll get down off my soapbox for a while!
