How to adjust timing if you can't see the timing marks?

Line up the mark on the damper with 0. Or for the best accuracy in the future, use a piston stop to find the TDC on #1. Then make a mark on the timing cover and damper where you can see them while using the timing light. Anywhere will do. Then, using the damper mark as the 0 reference, apply a timing tape on the damper.