(I just did all this on Friday on my parts car. I was yanking the heater/AC box out to get at the fan motor. WHICH OF COURSE I realized I could get out with three simple nuts from inside the engine compartment with no (zero) disassembly, it was smartly designed for replacement/service. D'OH!)
HAH!! I doubt it was designed for replacement service, just easy to put in on assembly line and happens to be easy to replace. But maybe the designer in charge of that particular item DID design it that way on purpose... Most parts are designed for easy assembly -- disassembly be d#$%ed! That's what they sell new cars for...
Well the blower fan is mounted on a disk of steel (8" - 10"), and fits into a hole in the back of the heater box, and they made it poke through the firewal, and the brake lines go around it so that it simply lifts out.
You gotta take the whole miserable thing out to get at the heater core, but the blower motor is easy!