How do I remove rear bumper on a 58 chevy I removed all 8 bolts but bumper will not come loose

Just a thought. Is there visible surface rust on frame? If so take a rubber mallet or something similar and give bumper a little bump or two. It's been on there a long time and might just be stuck due to years of use.

If the rubber mallet does not knock it lose, use a pry bar with the sharp flat end between the bumper and the bracket holding it in place. Lightly tap it to encourage the rust to let go. These bumpers were strong enough to jack up the car with, so try using a jack on the bumper to put a little weight on the bumper and see if that doesn't start it braking lose. Next would be a grinder to go around the edges, but that could be a disaster if done wrong. Try also putt9ing on rust be gone stuff ans see if that will help. 56 years of binding tight will make anything tough to remove.