Well, It took a few days or wrenching but I managed to replace the heater core. I had to remove all the lower A/C ductwork, the radio, the console, both front seats, the lower section of the passenger fender and inner fender, the rocker panel trim and bracket and several other things I am probably forgetting. None of the stuff showed any evidence of ever having been removed before. I was rather neat to see what the actual hardware was supposed to be rather than someone's version of what screw fits what hole.
I found some interesting things along the way...like this:
Notice anything odd about the Turbo 400 kickdown switch on the throttle cable bracket? Yeah, the portion of the harness was never connected to it. It is still dangling behind the steering column. (The orange and pink wires) There are no marks or scratches on either of the two terminals on the switch. So I hooked it up for future use.