Craig,

I have found that using a small flat head screw driver, or dental tool to scrape the carbon off the valves (after you have them out), then using a scotch brite pad to really polish them up will bring them back to as good as new.

You will also want to make sure the landings within the cylinders are clean or carbon so the power valves land cleanly and produce a nice smooth transition from cylinder/exhaust port to power valves.

as for the cylinder you have pics of, I wouldn't use those. The port walls look like too much material has been removed and the heat build up is causing the metal to weaken and crack. This can lead to further failure and damage.

You could have them welded up, cleaned up and replated, but you will most likely end up with the same issue in the end.
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Charles Gallant