I would measure the piston skirts and bores before buying pistons, seeing the top ring means nothing to me as that part of the piston is smaller. From what I see is it possible the head gasket was seeping when the car sat, or do you see a crack for sure? If it was seeping with the rusting and the white corrosion I think you found your problem, rings are ruined. If that is a crack, and that block is siamese, you had better magnaflux at least that bore,and the bore beside it. I would do them all.