I know of a quick easy way to tell if its the timing chain or not. Timing chains don't usualy JUMP a tooth unless they are streched out a lot. Take your distributor cap off, While watching the rotor turn the crank by hand back and forward. If you can turn the crank any distance in either direction and the rotor not turn then the chain is bad. Just a little somthing I got from playing with these engines for so long. If your engine has the orignal 67 T-chain then it probably is bad. Its only a few hr job.