In 1998 I did a 77 Corvette with the same problem, I was fortunate enough to have a large hot water tank with a temperature control (a friend of mine owned a chroming shop and they need hot water for rinsing) that I could drop the whole bumper into...when it came out I had 2 pieces of metal and body panel adhesive ready. I applied the body panel adhesive and the first piece of metal to the underneath of the warped bumper and put the other piece of metal on the top of the bumper and clamped the 2 together...let the adhesive cure, bolted it to the vette and it took minimal repair to the bumper after. I haven't seen the car for a few years now but I know it has lasted for over ten years....longer than the original.
Hope this helps Henry. The hard part here would be to find that tank.