It's true. The right side fender apron blocks any access to the heater blower motor. It can only be removed once you have access to all the screws under there, and you need clearance to get the motor out. I removed the fender apron with the fender on the car, but i don't recommend it. Take your fender off.

The heater core is mounted from inside the car as popptj said above. There are studs in the housing that pass through the firewall and nuts on the engine compartment side of the firewall holding it in.