A833 inside swap

Just out of curiosity, why does the input retainer have to fit perfectly in the bellhousing? The bolts that hold the trans to the bellhousing should locate it pretty accurately as well as the pilot bushing. I'm almost certain mine is no where close to being the same size, the trans is a 73 and the bellhousing I'm fairly sure it an OD aluminum setup. I haven't been running any adapter and so far it doesn't seem to give me any issues.