My 5.9 into '68 Dart swap

That piston ding and corresponding scratch could have been most anything from intake casting flash to a dropped and lost carb part.
The stain on the cylinder wall is the ghost from that part in the other cylinder that's restlessly wandering around.
You my friend have a haunted block. :D
(only thing I have ever seen make a mark like that was a hotspot) but who knows why until it gets checked out and refreshed.

Here's where you decide if you are going to stay within the budget or not.

I have seen people run a lot worse.