And also, please verify that you have the starter locating plate in between the bellhousing and the block.
Some folks like to think this is a shim or torque plate. But really it is what sets the distance for the starter from the center of the crankshaft..

You can run without it, but you'll either have to much or to little clearance. ALso used was special bolts, they have a larger head and a smaller diameter than the thread just below the head to allow the starter clearance to move to the correct location, indexed by the plate.