I need to do the same job, actually, though it's a long way down my list, so I haven't done it yet. Anyway, looking at the Helm's manual, it looks like you can pull the heater duct/evaporator and blower assembly by simply removing the glovebox and glovebox frame.
In fact, the blower motor fits in to the bottom of the blower assembly, so it's possible that you don't even need to pull the whole assembly. It's mostly a question of whether you'd have enough room to get the blower out and in while the assembly is still mounted on the car.
In any case, you certainly don't need to pull the whole dash apart. At minimum, I'd say you'll have to pull the glovebox, and at most, you'll also need to pull the duct and blower assembly.
Post back and let me know how it goes!