Could anyone tell me what the symptoms of a burnt exhaust valve are?

 

Check the compression on each cylinder. If you have a burnt valve, you won't have any compression on that cylinder. You'll also have a noticable loss in power (basically running on 7 cylinders instead of 8), and what will seem like a miss. Valves are easy to grind if you think you have a bad one. I used to do it all the time on my Ford 351 Windsors and 352 FE motors. I have never done a 318 or 360, but can't imagine it is any different.