If the woodruff key on the snout is screw up, they are more previlant on a 6 than most think, you can have a crank shop cut a new groove 180 degrees out and every thing will still match up.
Don't ever trust a timing mark....Do what was said above; screw something in the spark plug hole and hand crank until it hits. Make a mark on the the balencer. Rotate the crank in the opposite direction until it stops again. Make a second mark. Split the difference and that is TDC.
Good Luck
