I've had success cleaning up rusted cylinders on tractors. You can see the damage more clearly from the top, but it is going to look much worse initially than it really is since there is going to be slop on top of the pistons.
From the bottom you'll see some rust on the rods if there is much water present. If you see rust on the lower part of the cylinder, work it with some WD40 to see if it cleans. If not the top part of the cylinder is going to be very bad.
If there is water in the pan, and you are rebuilding away, use it as a bargaining point.
But the real mechanics will know if you can bore the cylinders to get past pitting.
