'79 Grand Prix won't start

]My car backfired 2 years ago & "died". We are trying to get it going again & can't get it to start. We had it running the other night for about 20 mins, then it stalled and we can't get it started again. We've replaced the battery, fuel pump, coil, rebuilt the carb, changed the plugs & wires. It cranks, but won't start. My son needs to take his car back to the base, so I need to get this car running. It's a 301/4.9 :banghead: . Thanks for any help or ideas!!

How's the timing? Is it possible the timing chain has slipped a notch?