Which bellhousing to use?

I was talking about the older bellhousings. I read that the smaller holes could be machined out to 4.80 ( any larger would go into the bolt holes ) and change the retainer on the O/D to 4.80. That way I could match an older bellhousing to the O/D if need be. But I would like to use the newer bellhousing with the 5.125, but I'm not sure it would fit my motor and car.