Patch it up and drive it, or bolt it together and drive it. The back bumper is not going to fall off, and there probably wouldn't be much difference in protection in the event of a rear collision either way.

If you can't do it yourself, find someone you trust and do as they suggest.

Really, how many people are going to climb under the car to see what it looks like (except other Mopar guys) and does it really matter to you what they think? What does their 56 year old car look like?

I'd probably bolt the bumper on and drive the wheels off of it, and would enjoy every minute behind the wheel.