That's not surprising. I couldn't quite see the number on the piston, but I think there's an above picture of cylinder #7 with the piston still in it. There's one BIG ridge in that cylinder. To me, that looks like a lot of miles or dirt being sucked in through the air filter. If that's the only cylinder with that bad of a ridge, my only guess would be that the injector may have been leaking for a long time and got that cylinder too hot. Maybe that could have made the ridge somehow?
Not really if you consider the way that the "V" engines work. The reason why inline engines, Cummins included, last longer than a V style engine (usually) isn't because they're a superior engine, it's due to cylinder wear. In an inline engine, the pistons move up and down with minimal side pressure on the cylinders. In a V style engine, the pistons put more side pressure on the cylinder walls that are the farthest away from the crankshaft. This is because while the crank is rotating, it's pushing the pistons up and down, but also to the side since the pistons don't move straight up and down. This is why you only have a bad ridge on the side of the cylinder that's opposite from the crankshaft, toward the outside of the engine, not toward the center. The "waves" in your cylinders are different ring ridges. This makes me lean toward a very high mile engine. It also had the original style head gaskets due to the orange "stuff" left over on the block after you removed them. I didn't say that the head gaskets were the original ones. They could have been replaced with OEM gaskets in the past.
You're not quite grasping the concept here. These block and cylinders are one piece from the factory. Like a gas engine is made. They do not have liners from the factory like heavier duty diesel engines do. Sleeves are used to bring the cylinders back to the stock bore size when the cylinders have too much wear in them. What happens is that the machinist overbores the cylinders. Then the sleeves are press fitted into the block. The cylinders are bored to just slightly, maybe only .001", smaller than the outside diameter of the sleeves which is what keeps the sleeves in place. I believe that the sleeves actually have to be bored out a little bit to make them the stock bore size after they're installed. It's a more complicated process than replacing the liners in a heavier duty diesel engine.