Ok, for a start you will find those aren't cracks. That looks normal inside a honda, I have questioned it myself many times. Now for it to bend a valve like that and move a guide, I would say the timing belt has either let go or slipped a few notches. Really the only way you will get damage like that is if the piston hits the valve.
Personally as far as i have ever known GCV engines are a throw away. By the time you replaced the cylinder (99% sure guides are not available as a part for those) valve, rocker, belt, cam, maybe a gasket (mostly glued together) you will be looking at a lot of money. not to mention if you are having belt troubles it would indicate it has done quite a bit of work so you may even be looking at rings etc.
That's good news!
The valve isn't noticeably bent. I need to take a straight edge to it. I think what happened is there's enough build up on the valve stems that it simply got stuck. It also didn't look like the belt slipped or anything. Right now I'm trying to find out what Honda part 12000-Z8D-010 includes and doesn't include.
