Pretty much agree with Tintin on the assesment. The pistons are aluminum. So, they don't rust. But, they can corrode, and that is usually white in color. The rings are unuseable. The ring lands in the pistons can be damaged by the expanding rust of the rings.
The real issue is the cylinder walls. These will have to be, at least, honed. After honing to good base metal then measured. If still within serviceable limits, they can be reused, with perhaps the old pistons if they examine well after cleanup. If not, then bored to the next over size. But, you should find a set of pistons and rings for it first, and have it bored to fit them.
As for the valves, the surface rust shown doesn't bother me. But, the valve seats and valve mating faces should be carefully examined after cleaning. They may need regrinding and lapping on number one. And you may as well address the others while broken down to this stage. Just remember that if you take parts out of the assembly to note where they came from so they can be assembled in the same positions they were before, as the bearing surfaces have already worn as a mate. In other words, don't move valves from cylinder to cylinder, for example.
