The good:
Thought I had to buy a torx driver, but the tool kit I got years ago for building PCs turned out to have the size I needed to get into the A500.
The bad:
The center rear screw is rusted. The other screws are fine. I'm letting it soak in liquid wrench until tomorrow. If I can't muscle it open, it's time to Dremel a slot for a normal screwdriver.