Flywheel locks after Bolting Bellhousing?

If the flywheel doesn't spin when you tighten the bell. You have a 69 or earlier 11.5 flywheel with a 70 or later 10 1/2 bell housing. Count the teeth on the flywheel 143 is the 60 or early flywheel and 130 is the later style. You have to use the correct bell for the flywheel your using.