Yeah man, go to Kragen or Autozone and get that Airplane stripper. I used it on my 72 Gran Torino and the older paints just came off. What we did was apply the "Paint Thinner" and then gave it about 15-20 mins to soak into all the paints, you should see the paints start to mold up, then some people just wash the thinner off, but since my 72 was old kinda like your 51, the paint was stuck on. So we proceeded to use those metal spatulas to get the paint off but if you do use the spatulas to take the paint off, dont do it so rough
because you will leave like deep scratches in the metal. I let my friend try to help me and dad on the project and he ended up leaving a bunch of scratches on my Torino, we used about 2 coats of primer to fill up the deep scratches so thank god for primer! haha. Well i hope this info was somewhat useful.