Backplate won't come off?

I have an old LTD H-51 that I'm trying to disassemble so I can paint, but the backplate won't come off no matter what I do. I've tried pulling it off with tape, prying it off eith a knife (even my sharpest knives were too thick to wedge under it, screwing a screw slightly into the backplate and prying it from the screw, but it won't budge one bit. Any tips? Is the backplate perhaps not designed to come off of this particular model (I couldn't imagine but you never know)?