I can see the diff shapes, but can't get the reason for that.

440 source states the ones they are selling are the same but just the spacer to mark the diff side.... aside the mount offset provissions, since mount is the same for both sides but turned around ( hence the offset holes made diff )

http://store.440source.com/Engine-Support-Brackets-66-72B-66-73C-70-74E/productinfo/119%2D1000/