there is sometimes a witness mark on the back side of the flywheel where it mates up to the crank. Look at the crank and flywheel. Some of them had maybe a little half-drilled hole in the crank, and that hole would leave a witness mark on the flywheel. Line em up and hand tighten all bolts.
ONE of the 6 bolt holes is not the same distance apart as the others and it's kind of a pain to line em all up.