GROAN....whatta PITA!
After removing all the screws, including the ones you can barely find, let alone see, I managed to get the dashpad out.
Yes, that's RUST. Toyota applied NO protective dip, coating, or paint on the steel parts behind the dash, and they start returning to their native state after a few years. Now I don't need to pull all these rusty bits to swap out the heater core, but they're coming out and getting sandblasted. I'll ask my guy at the powder coating place how much extra it will cost to have them powder coated vs my buying numerous cans of paint at $20 a pop. I'm guessing I'll just get them coated, as that way they're ready to go back in the car as soon as I get them home, versus taking a week or more to get them primed, cured, painted, and the paint cured.
SLW was worried I'd get Tetanus working in there until I reminded her that I had a TDAP shot six months ago.
Since the instrument cluster is out, I'm going to put new lamps in it, remove the plastic cover for polishing, and clean 40 years of dust (and two dead bugs!) out of it.