Did you check your timing marks before you removed the chain and gears? Were they off, even a little bit? Low compression readings can be accounted for by the chain being off by a tooth or two, but any more than that and you would be getting much lower than that. 115-120 is a little low, but I’m not sure it is low enough to account for the engine jumping time. It seems more like typical wear on an old engine. Based on the engine in the truck and what you experienced, the central fuel injection unit is definitely suspect. A leak out of that will cause backfiring and failure to start due to a seriously over-rich condition. I would still try putting it back together and trying to start it. If you still don’t have spark, I would try a new ignition module. They are cheap and easy to replace, probably cheaper than the coil you didn’t need. If you didn’t pull the distributor, I would recommend against doing it. There should be no need to do it, and getting it to go back in will be tough if you are ‘new to cars.’