1968/72 Pontiac Firebird #1576864585

I ask this question on behalf of my father who is to stubborn to ask any one. So my dad has a “68” firebird with a 400 motor. however it is more of a 72 since the motor, trany, etc, is from the 72. I would like to fix it for him so I can move it and park my Daytona where it currently is. There are two major problems as far as I can tell.

Problem 1: it does not start. You turn the key and get a click but nothing else. I have changed the starter, check the battery and connections, and even looked at the Neutral safety switch. But I can’t get it to turn over. It will start up sometimes out of the blue but there is no pattern to when it works.

Problem 2: this is the most recent problem. So my dad had it at storage and after repeated attempts all day we finally got it running. So we pull it out and start driving. It was running rough. It sounded like it was struggling to stay running. Then we got it up to 45 mph and all hell broke loose. It started backfiring, dying out, and final came a loud boom. I was looking out the window when the big boom came and I could see fire burst out from under the car. We pull over, leave it running (my dad didn’t want to shut it off because he didn’t know if he could start it again) and while was still running horrible it was not on fire. We attempted to limp it back to storage but it finally died and we needed a tow. My dad though it was the carburetor. That maybe true but I just need a second opinion.

The car is a bit of a mess so these could be two separate problems or possibly related. If anyone has any ideas or may know the problem, I would greatly appreciate your advice.
Thanks,
Mark I

Duplicate post.