I'm no expert, but it does sound like timing may be a problem. When you had the timing light on it, I presume you had the car at idle, warmed up, and the vacuum advance line plugged up. Did you rev up the engine to see if the timing advanced via the mechanical advance in the distributor? If it advanced quite abit (I'm guessing about 10 degrees more) then it is probably working OK. Then connect the vacuum advance line back to the dizzy. Rev it up again, it should advance even more, (maybe another 5-10 degrees) if so, it is working OK. Good luck, don't give up yet, it probably is some simple little thing and you'll feel real good about yourself once you find it.