I think your pistons look pretty new. If the engine has not been rebuilt I think you have a VERY low mileage engine. That rod bearing looks bad, may indicate an oiling problem at some point. They are not terrible, but I don't think it's normal wear. It's not uncommon for the crank to be good, even with some bearing wear, but you won't know until you look at the mains.
Check your ring gaps, and measure your piston to bore clearance. Check the piston diameter on the thrust surfaces, not at the pin bores. I would be very surprised if you couldn't reuse your pistons. If you didn't do a leak down test before you took the engine apart you missed an opportunity to pinpoint your low power condition. So far, from the pics you've posted, it doesn't look like you have any major mechanical issues, and certainly not excessive wear.
You can do a rudimentary check of the condition of your valves/seats on the bench. Just reinstall the valves (don't bother to install new guide seals yet) and see if they leak when you pour alcohol in the ports. If they do leak you'll know you need a valve job. If they don't, you should probably get them cleaned up anyway, but in any event they aren't real bad.
