I remember a neighbor coming over to me many years ago, telling me that he'd just replaced all the plug wires on his V8 truck. When he tried to start it he said it backfired once and then wouldn't start.
I went over and looked at what he'd done. He said that he followed the cylinder numbers on the engine block and connected the wires in order 1-2-3-4, etc. I explained that it doesn't work that way and I pointed to the firing order stamped on the block.
Not saying that's what the problem is here but it brought back memories.