That's not the worst scoring I've seen, by a long shot. But it's not pretty. I'd say somebody ran that machine a while very low on oil.
The piston looks much better that the earlier pic, that must have been dirt/oil on there.
Cheapest fix: Put new rings in, put it all back together, pretend you never saw it, and use the machine for the next 10 years
I suspect you don't want to go that cheap. In that case, mic it first, to see how worn it is. If it's within spec, or even close to it, hone it, in particular the top of the bore where the scoring is worst. I wouldn't try for a glass smooth finish, just clean enough that when you run your fingernail over it it doesn't feel rough. Replace piston and rings.
The really correct fix, it's it's worn past spec, would be to bore it. Then hone, new piston etc.
If it was my machine, and it had been running beforehand, I'd try to go for the cheap fix.
[Later] Actually, that's not quite right. I'd hone it to remove the rough stuff, esp at the top. And I would mic it. But I don't believe it's too far out, based on that marks on the piston and jug. So if it mic'ed out reasonably ok, I'd just hone it and put rings in it and be done with it.