Block out of square

The other reason you can't use shims is that the shims would have to be tapered in order to work properly even though it would still put excessive force around the bolt holes. Tapered shims of the exact perfect thickness and taper would be difficult you machine/get??? A shim that has sides that are parallel would greatly increase the chances of bell housing breakage because you would have one side "dead" veritical (the block face) and and one side at an angle (the bell face) while the shims would have parallel faces. This would not be a good scenario??? Treblig