I'm with Toby in that basically everything looks like it's in plenty good shape to keep using. On the other hand, if you've already got the engine out and torn apart, why not go ahead and replace those bits? It's not easier to put an old part back on than a new one, so for everything that's already off, it's only a question of $, and the sprocket, chain, and guides aren't exactly what I would call pricy bits. Pistons are a bit more costly though, and of course the whole availability thing is another matter. FWIW, when I rebuilt my engine, I changed from a double row to single row chain, primarily because the single row stuff cost half as much as new double row components, so it was easier to swallow the cost for new parts rather than reusing the old ones, which (similar to yours) probably still had a good amount of life left in them.