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.
