If you have a non-A/C car (maybe one with A/C, I'm not sure), you can bypass the core just by re-routing the heater hoses under the hood.
I replaced my core when I removed my dashboard for restoration. There is access to removed the blower motor from under the hood--a pretty tough job I hear, and it's pretty small compared to the coil.
I removed the heater box after the dash was out. It wasn't easy. They say it can be removed with the dash still in the car, though I have no idea how.
Good luck!
~Steve
P.S. The heater box removed from the car:
Here it is in place. It extends from the passenger door all the way over to the driver's side heat vent, and it's all one piece!
