OMG need help fast

Do a compression test and a leak down test (If you have the tester). Most likely you have a burnt valve or if the engine is pre unleaded you have a sunken seat. During a leak down test you can hear where the air is escaping and will be able to tell where the problem is. Swap the plug for that hole. If the miss follows the plug then the plug is bad. Swap the wire with another spark plug wire. If the miss follows, then the plug wire is NG. If you have a bad timing chain sometimes you will have low compression accross the board but being the miss has been isolated to 1 cylinder, it's most likely not a timing chain. (but with that many miles on a silent chain, it probably needs to be replaced.) You have already checked the rockers and make sure you check the valve springs and retainer. If you do the leak down test and the cyl is showing that it is holding compression and you can't find any other problems, you might have a bad cam.